U.S. patent number 9,181,169 [Application Number 13/888,542] was granted by the patent office on 2015-11-10 for process for heterogeneously catalyzed gas phase partial oxidation of (meth)acrolein to (meth)acrylic acid.
This patent grant is currently assigned to BASF SE. The grantee listed for this patent is BASF SE. Invention is credited to Nina Blickhan, Alfons Drochner, Nadine Duerr, Tim Jekewitz, Andrey Karpov, Nadine Menning, Klaus Joachim Mueller-Engel, Tina Petzold, Frank Rosowski, Sabine Schmidt, Herbert Vogel, Cathrin Alexandra Welker-Nieuwoudt.
United States Patent |
9,181,169 |
Welker-Nieuwoudt , et
al. |
November 10, 2015 |
Process for heterogeneously catalyzed gas phase partial oxidation
of (meth)acrolein to (meth)acrylic acid
Abstract
A process for preparing (meth)acrylic acid by heterogeneously
catalyzed gas phase partial oxidation of (meth)acrolein over a
multimetal oxide composition which comprises the elements Mo, V and
W and is obtained by a hydrothermal preparation route, and the
multimetal oxide composition obtainable by this preparation
route.
Inventors: |
Welker-Nieuwoudt; Cathrin
Alexandra (Birkenheide, DE), Karpov; Andrey
(Metuchen, NJ), Rosowski; Frank (Berlin, DE),
Mueller-Engel; Klaus Joachim (Stutensee, DE), Vogel;
Herbert (Nauheim, DE), Drochner; Alfons
(Niedernhausen, DE), Blickhan; Nina (Babenhausen,
DE), Duerr; Nadine (Alsbach-Haehnlein, DE),
Jekewitz; Tim (Frankfurt, DE), Menning; Nadine
(Darmstadt, DE), Petzold; Tina (Darmstadt,
DE), Schmidt; Sabine (Darmstadt, DE) |
Applicant: |
Name |
City |
State |
Country |
Type |
BASF SE |
Ludwigshafen |
N/A |
DE |
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Assignee: |
BASF SE (Ludwigshafen,
DE)
|
Family
ID: |
46509764 |
Appl.
No.: |
13/888,542 |
Filed: |
May 7, 2013 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20140018572 A1 |
Jan 16, 2014 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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61645082 |
May 10, 2012 |
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Foreign Application Priority Data
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May 10, 2012 [DE] |
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10 2012 207 811 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01J
37/0009 (20130101); C07C 51/16 (20130101); C01G
39/00 (20130101); B01J 37/0036 (20130101); C01G
41/006 (20130101); B01J 37/0221 (20130101); B01J
35/1014 (20130101); B01J 23/002 (20130101); B01J
35/023 (20130101); B01J 37/04 (20130101); B01J
35/002 (20130101); B01J 37/033 (20130101); C07C
51/252 (20130101); B01J 37/10 (20130101); B01J
37/0223 (20130101); B01J 23/30 (20130101); B01J
23/8885 (20130101); B01J 37/0045 (20130101); C08F
220/06 (20130101); B01J 37/06 (20130101); B01J
37/08 (20130101); C07C 51/235 (20130101); C07C
51/252 (20130101); C07C 57/04 (20130101); C07C
51/235 (20130101); C07C 57/04 (20130101); C01P
2006/12 (20130101); C01P 2002/72 (20130101); B01J
2523/00 (20130101); B01J 2523/00 (20130101); B01J
2523/55 (20130101); B01J 2523/68 (20130101); B01J
2523/69 (20130101); B01J 2523/00 (20130101); B01J
2523/17 (20130101); B01J 2523/55 (20130101); B01J
2523/68 (20130101); B01J 2523/69 (20130101) |
Current International
Class: |
C07C
51/16 (20060101); B01J 37/04 (20060101); B01J
37/06 (20060101); B01J 37/08 (20060101); B01J
37/10 (20060101); C01G 39/00 (20060101); C01G
41/00 (20060101); C08F 220/06 (20060101); C07C
51/25 (20060101); B01J 37/03 (20060101); B01J
23/00 (20060101); B01J 37/02 (20060101); C07C
51/235 (20060101); B01J 23/30 (20060101); B01J
23/888 (20060101); B01J 35/00 (20060101); B01J
35/02 (20060101); B01J 35/10 (20060101); B01J
37/00 (20060101) |
Field of
Search: |
;562/532,535 |
References Cited
[Referenced By]
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Nov 2006 |
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WO |
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Other References
English translation of Dieterle et al. from a website titled
Espacenet, translated on Apr. 25, 2014. cited by examiner .
International Search Report issued Sep. 30, 2013 in
PCT/EP2013/058849 (with English translation of Category of Cited
Documents). cited by applicant .
U.S. Appl. No. 14/535,743, filed Nov. 7, 2014, Macht, et al. cited
by applicant .
U.S. Appl. No. 14/536,969, filed Nov. 10, 2014, Macht, et al. cited
by applicant.
|
Primary Examiner: Valenrod; Yevegeny
Assistant Examiner: Doletski; Blaine G
Attorney, Agent or Firm: Oblon, McClelland, Maier &
Neustadt, L.L.P.
Claims
The invention claimed is:
1. A process, comprising heterogeneously catalyzing a partial
oxidation of (meth)acrolein to (meth)acrylic acid in the gas phase
over a catalytically active multimetal oxide composition of formula
(I):
Mo.sub.12V.sub.aX.sup.1.sub.bX.sup.2.sub.cX.sup.3.sub.dX.sup.4.sub.eX.sup-
.5.sub.fX.sup.6.sub.gO.sub.n (I), wherein: X.sup.1 represents W,
Nb, Ta, Cr, Ce, or a mixture thereof; X.sup.2 represents Cu, Ni,
Co, Fe, Mn, Zn, or a mixture thereof; X.sup.3 represents Sb, Te,
Bi, or a mixture thereof; X.sup.4 represents H, one or more alkali
metals, or a mixture thereof; X.sup.5 represents one or more
alkaline earth metals; X.sup.6 represents Si, Al, Ti, Zr, or a
mixture thereof; a represents 1 to 6; b represents 0.2 to 8; c
represents 0 to 18; d represents 0 to 40; e represents 0 to 4; f
represents 0 to 4; g represents 0 to 40; n represents a number
determined by the valency and frequency of the elements in the
formula (I) other than oxygen; at least 50 mol% of a total molar
amount of elements X.sup.1 present in the multimetal oxide
composition of formula (I) is the element W; the multimetal oxide
composition of formula (I) is prepared by hydrothermally treating a
mixture of sources of elemental constituents in the presence of
water in a pressure vessel, such that a newly forming solid is
removed as a precursor composition which is converted to the
catalytically active multimetal oxide composition of formula (I) by
thermal treatment; and an aqueous mixture subjected to the
hydrothermally treating at 25.degree. C. and 103.1 kPa has a pH of
.gtoreq.1 and .ltoreq.3.
2. The process according to claim 1, wherein the catalytically
active multimetal oxide composition satisfies formula (II):
Mo.sub.12V.sub.aX.sup.1.sub.bX.sup.2.sub.cX.sup.4.sub.eX.sup.5.sub.fX.sup-
.6.sub.gO.sub.n (II), wherein: X.sup.1 represents W, Nb, or a
mixture thereof; X.sup.2 represents Cu, Ni, or a mixture thereof;
X.sup.4 represents H; X.sup.5 represents Ca Sr, or a mixture
thereof; X.sup.6 represents Si, Al, or a mixture thereof; a
represents 2 to 4; b represents 0.2 to 3; c represents 0.5 to 3; e
represents 0 to 2; f represents 0 to 0.5; g represents 0 to 8; and
n represents a number determined by the valency and frequency of
the elements in the formula (II) other than oxygen.
3. The process according to claim 2, wherein at least 50 mol% of a
total molar amount of elements X.sup.2 present in the multimetal
oxide composition of formula (II) is the element Cu.
4. The process according to claim 1, wherein the catalytically
active multimetal oxide composition satisfies the formula (III):
Mo.sub.12V.sub.aW.sub.bCu.sub.cX.sup.4.sub.eX.sup.5.sub.fX.sup.6.sub.gO.s-
ub.n (III), wherein: X.sup.4 represents H, one or more alkali
metals, or a mixture thereof; X.sup.5 represents one or more
alkaline earth metals; X.sup.6 represents one or more selected from
the group consisting of Si, Al, Ti and Zr; a represents 2 to 4; b
represents 0.2 to 3; c represents 0.5 to 2; e represents 0 to 4; f
represents 0 to 4, with the proviso that a sum of e and f does not
exceed 4; g represents 0 to 40; and n represents a number
determined by the valency and frequency of the elements in the
formula (III) other than oxygen.
5. The process according to claim 1, wherein the hydrothermally
treating occurs at temperatures in the range of >100.degree. C.
to 600.degree. C.
6. The process according to claim 1, wherein the hydrothermally
treating occurs at a superatmospheric working pressure of
.ltoreq.50 MPa.
7. The process according to claim 1, wherein, based on amounts of
water and sources of the elemental constituents present in the
pressure vessel during the hydrothermally treating, a proportion by
weight of a total amount of the sources is 3 to 60% by weight.
8. The process according to claim 1, wherein at least one source of
the vanadium of the formula (I) comprises vanadium in the +4
oxidation state.
9. The process according to claim 1, wherein removal of the solid
newly forming in the hydrothermally treating comprises at least one
mechanical removal of the solid and at least one washing operation
on mechanically removed solid with at least one wash liquid
selected from the group consisting of an organic acid, an inorganic
acid and an aqueous solution thereof.
10. The process according to claim 1, wherein a temperature of
hydrothermally treating is 350 to 650.degree. C.
11. The process according to claim 1, wherein the catalytically
active multimetal oxide composition is an active composition of an
eggshell catalyst in which it has been applied to the surface of a
support body.
12. The process according to claim 1, wherein a specific surface
area of the active multimetal oxide composition is .gtoreq.15
m.sup.2/g.
13. The process according to claim 1, wherein b is 0.2.
14. The process according to claim 1, comprising heterogeneously
catalyzing a partial oxidation of acrolein to acrylic acid.
Description
The present invention relates to a process for heterogeneously
catalyzed gas phase partial oxidation of (meth)acrolein to
(meth)acrylic acid over a catalytically active multimetal oxide
composition of the general formula I
Mo.sub.12V.sub.aX.sup.1.sub.bX.sup.2.sub.cX.sup.3.sub.dX.sup.4.-
sub.eX.sup.5.sub.fX.sup.6.sub.gO.sub.n (I) in which the variables
are each defined as follows: X.sup.1=W, Nb, Ta, Cr and/or Ce,
X.sup.2=Cu, Ni, Co, Fe, Mn and/or Zn, X.sup.3=Sb, Te and/or Bi,
X.sup.4=one or more alkali metals (Li, Na, K, Rb and/or Cs) and/or
H, X.sup.5=one or more alkaline earth metals (Mg, Ca, Sr and/or
Ba), X.sup.6=Si, Al, Ti and/or Zr, a=1 to 6, b=0.2 to 8, c=0 to 18,
d=0 to 40, e=0 to 4, f=0 to 4, g=0 to 40, and n=a number which is
determined by the valency and frequency of the elements in I other
than oxygen.
(Meth)acrylic acid is used in this document as abbreviated notation
for "acrylic acid and/or methacrylic acid".
(Meth)acrolein is used in this document as abbreviated notation for
"acrolein and/or methacrolein".
Acrylic acid and methacrylic acid are important monomers which find
use for preparation of polymers, for example, as such, in the form
of their alkyl esters and/or in the form of their alkali metal
salts. Depending on the specific (meth)acrylic monomers used to
form the respective polymer, it can be used, for example, as an
adhesive, or as Plexiglas.RTM., or as a superabsorbent for water or
aqueous solutions.
The preparation of (meth)acrylic acid by heterogeneously catalyzed
gas phase partial oxidation of (meth)acrolein is common knowledge
(cf., for example, WO 2004/031114 A1, EP 714700 A2, DE 4431949 A1,
DE 3030243 A1, DE 3030243 A1 and the literature cited in these
documents), and is of significance especially as the second
oxidation stage in the preparation of (meth)acrylic acid by
two-stage heterogeneously catalyzed gas phase partial oxidation
proceeding from propene or from isobutene. It is also known that
multimetal oxide compositions of the general formula I can be used
as catalytically active compositions for the heterogeneously
catalyzed partial gas phase oxidation of (meth)acrolein to
(meth)acrylic acid (cf., for example, DE 102007010422 A1, DE
102010023312 A1, Applied Catalysis A: General 269 (2004), pages 53
to 61 and Applied Catalysis A: General 325 (2007), pages 237 to
243).
The starting materials used for preparation of these multimetal
oxide active compositions are sources (starting compounds) of the
elemental constituents other than oxygen in the desired multimetal
oxide active composition in the respective stoichiometric ratio
desired in the multimetal oxide active composition, and these are
used to obtain a very intimate, preferably finely divided, dry
mixture which is subsequently converted to an active oxide by
thermal treatment. The sources may either already be oxides or may
be those compounds which can be converted to oxides by heating, at
least in the presence of oxygen.
The intimate mixing of the starting compounds (sources) can be
effected in dry or wet form. If it is effected in dry form, the
sources (starting compounds) are appropriately used in the form of
fine powders and, after mixing (and optionally compaction for the
purpose of powder coarsening), subjected to thermal treatment.
The intimate mixing in the prior art preparation processes,
however, is preferably effected in wet form, and appropriately for
application purposes in aqueous form. This involves mixing the
starting compounds with one another in the form of a solution
and/or suspension (e.g. aqueous solution and/or suspension).
Subsequently, the wet composition (solution or suspension) (e.g. an
aqueous composition (solution or suspension)) is dried and the
resulting intimate dry mixture (optionally after intermediate
compaction for the purpose of powder coarsening) is thermally
treated. Particularly intimate dry mixtures are obtained in the
mixing process described when the starting materials are
exclusively sources (starting compounds) present in dissolved form.
The drying operation is preferably effected by spray drying.
A characteristic feature of the prior art mode of production
described is that all preparation steps (apart from any
intermediate step for powder compaction employed for coarsening
purposes) are conducted at atmospheric pressure.
However, a disadvantage of processes for heterogeneously catalyzed
gas phase partial oxidation of (meth)acrolein to (meth)acrylic acid
over multimetal oxide compositions of the general formula I
obtainable as described as catalytically active compositions is
that both the selectivity of target production formation (of
(meth)acrylic acid formation) for a given conversion of the
(meth)acrolein and the conversion of (meth)acrolein established for
a given reaction temperature, and hence the activity of the
catalytically active composition, are not entirely satisfactory.
Both shortcomings are disadvantageous for a process for
heterogeneously catalyzed partial gas phase oxidation of
(meth)acrolein to (meth)acrylic acid in that they reduce the
resulting yield of (meth)acrylic acid. (Yield A (mol %)=selectivity
S (mol %).times.conversion C (mol %)/100 mol %).
Catalysis Today 91-92 (2004), page 237 to 240, describes the
hydrothermal preparation of a mixed oxide
Mo.sub.12V.sub.3.48O.sub.x and the use thereof as a catalytically
active composition for the heterogeneously catalyzed partial gas
phase oxidation of acrolein to acrylic acid.
WO 2005/120702 A1 and EP 1407819 A2 relate to the hydrothermal
preparation of multimetal oxide compositions which have, as base
elements, likewise the elements Mo and V, but not the element W.
Broadening of the base is undertaken in these documents primarily
with the elements Nb and the elements Te and/or Sb. In both
documents, the use of such multimetal oxide compositions as
catalytically active compositions for a heterogeneously catalyzed
partial gas phase oxidation of hydrocarbons, especially saturated
hydrocarbons, is at the forefront. Usability of such mixed oxides
as catalytically active compositions for a heterogeneously
catalyzed partial gas phase oxidation of (meth)acrolein to
(meth)acrylic acid is mentioned merely in passing in both
documents.
A disadvantage of processes for heterogeneously catalyzed partial
gas phase oxidation of (meth)acrolein to (meth)acrylic acid using
the hydrothermally produced mixed oxides detailed above as
catalytically active compositions is, however, that the catalytic
performance declines at a comparatively early stage in the
long-term operation of these processes.
It was therefore an object of the present invention to provide a
process for heterogeneously catalyzed gas phase partial oxidation
of (meth)acrolein to (meth)acrylic acid including the catalytically
active multimetal oxide compositions required therefore, which has
the described disadvantages of the corresponding prior art
processes and of the active compositions used in these processes to
a reduced degree at worst.
Accordingly, a process is provided for heterogeneously catalyzed
gas phase partial oxidation of (meth)acrolein to (meth)acrylic acid
over a catalytically active multimetal oxide composition of the
general formula I
Mo.sub.12V.sub.aX.sup.1.sub.bX.sup.2.sub.cX.sup.3.sub.dX.sup.4.sub.eX.s-
up.5.sub.fX.sup.6.sub.gO.sub.n (I) in which the variables are each
defined as follows: X.sup.1=W, Nb, Ta, Cr and/or Ce, X.sup.2=Cu,
Ni, Co, Fe, Mn and/or Zn, X.sup.3=Sb, Te and/or Bi, X.sup.4=one or
more alkali metals (Li, Na, K, Rb and/or Cs) and/or H, X.sup.5=one
or more alkaline earth metals (Mg, Ca, Sr and/or Ba), X.sup.6=Si,
Al, Ti and/or Zr, a=1 to 6, b=0.2 to 8, c=0 to 18, d=0 to 40, e=0
to 2, f=0 to 4, g=0 to 40, and n=a number which is determined by
the valency and frequency of the elements in I other than oxygen,
wherein at least 50 mol % of the total molar amount of elements
X.sup.1 present in the multimetal oxide composition (I) is
accounted for by the element W, and the multimetal oxide
composition (I) is prepared by a process in which a mixture of
sources of the elemental constituents of the multimetal oxide
composition (I) is subjected to a hydrothermal treatment in the
presence of water in a pressure vessel (as an aqueous mixture), the
newly forming solid is removed as a precursor composition and the
precursor composition is converted to the catalytically active
multimetal oxide composition (I) by thermal treatment.
Preferably in accordance with the invention, at least 60 mol %,
more preferably at least 70 mol %, even more preferably at least 80
mol %, or at least 90 mol %, and at best at least 95 mol %, or 100
mol %, of the total molar amount of elements X.sup.1 present in the
multimetal oxide composition (I) is accounted for by the element W.
These statements have general validity in this document
irrespective of the rest of the composition of the multimetal oxide
composition (I).
Advantageously, the stoichiometric coefficient b is 0.2 to 4 and
particularly advantageously 0.2 to 3.
The stoichiometric coefficient c is preferably 0.5 to 18, more
preferably 0.5 to 10 and most preferably 0.5 to 3.
The stoichiometric coefficient a is, advantageously in accordance
with the invention, 1 to 5, and particularly advantageously 2 to
4.
Preferably in accordance with the invention, the stoichiometric
coefficient d has values of 0 to 20, more preferably values of 0 to
10, and most preferably values of 0 to 2.
The stoichiometric coefficient e and the stoichiometric coefficient
f are (each independently) advantageously 0 to 2.
The stoichiometric coefficient g is advantageously 0 to 15 and
particularly advantageously 0 to 8. X.sup.1 is, advantageously in
accordance with the invention, W, Nb and/or Cr, and particularly
advantageously W and Nb, or (only) W. X.sup.2 is, advantageously in
accordance with the invention, Cu, Ni, Co and/or Fe, and
particularly advantageously Cu and/or Ni, or (only) Cu, X.sup.3 is,
advantageously in accordance with the invention, Sb, X.sup.4 is,
advantageously in accordance with the invention, Na, K and/or H,
X.sup.5 is, preferably in accordance with the invention, Ca, Sr
and/or Ba, X.sup.6 is, preferably in accordance with the invention,
Si, Al and/or Ti, and more preferably Si and/or Al.
Preferred multimetal oxide compositions (I) include those in which
the variables are each defined as follows: X.sup.1=W, Nb and/or Cr,
X.sup.2=Cu, Ni, Co and/or Fe; preferably at least 50 mol %, better
at least 70 mol %, and even better at least 90 mol % or 100 mol %
of the total amount of elements X.sup.2 present is accounted for by
the element Cu, X.sup.3=Sb, X.sup.4=Na, K and/or H, X.sup.5=Ca, Sr
and/or Ba, X.sup.6=Si, Al and/or Ti, a=1 to 5, b=0.2 to 4, c=0.5 to
18, d=0 to 10, e=0 to 2, f=0 to 2, g=0 to 15, and n=a number which
is determined by the valency and frequency of the elements in the
general formula I other than oxygen.
A group of multimetal oxide compositions (I) preferred in
accordance with the invention satisfies the general stoichiometry
II
Mo.sub.12V.sub.aX.sup.1.sub.bX.sup.2.sub.cX.sup.4.sub.eX.sup.5.sub.fX.sup-
.6.sub.gO.sub.n (II) in which the variables are each defined as
follows: X.sup.1=W and/or Nb, X.sup.2=Cu and/or Ni; preferably at
least 50 mol %, better at least 70 mol %, and even better at least
90 mol % or 100 mol % of the total molar amount of elements X.sup.2
present is accounted for by the element Cu, X.sup.4=H, X.sup.5=Ca
and/or Sr, X.sup.6=Si and/or Al, a=2 to 4, b=0.2 to 3, c=0.5 to 3,
e=0 to 2, f=0 to 0.5, g=0 to 8, and n=a number which is determined
by the valency and frequency of the elements in the general formula
II other than oxygen.
Another group of multimetal oxide compositions (I) preferred in
accordance with the invention satisfies the general stoichiometry
III
Mo.sub.12V.sub.aW.sub.bCu.sub.cX.sup.4.sub.eX.sup.5.sub.fX.sup.6.sub.gO.s-
ub.n (Ill) in which the variables are each defined as follows:
X.sup.4=one or more alkali metals (Li, Na, K, Rb and/or Cs) and/or
H, X.sup.5=one or more alkaline earth metals (Mg, Ca, Sr and/or
Ba), X.sup.6=one or more elements from the group of Si, Al, Ti and
Zr, a=2 to 4, b=0.2 to 3, c=0.5 to 2, e=0 to 4, f=0 to 4, with the
proviso that the sum of e and f does not exceed 4, g=0 to 40, and
n=a number which is determined by the valency and frequency of the
elements in the general formula III other than oxygen (or, in other
words: the stoichiometric coefficient of the element oxygen, which
is determined by the stoichiometric coefficients of the elements
other than oxygen and the valency thereof in the general formula
III).
Preferably in accordance with the invention, the stoichiometric
coefficient b in the general formula III is 0.5 to 2 and more
preferably 0.75 to 1.5.
Preferably in accordance with the invention, the stoichiometric
coefficient a in the general formula III is 2.5 to 3.5.
Preferably in accordance with the invention, the stoichiometric
coefficient c in the general formula III is 1 to 1.5.
Elements X.sup.4, X.sup.5 and X.sup.6 need not necessarily be part
of the catalytically active multimetal oxide compositions of the
general formula I (or of the general formula II or of the general
formula III).
Elements X.sup.6 within a catalytically active multimetal oxide
active composition of the general formula I act essentially as
inert diluents. As a result of incorporation thereof into the
catalytically active multimetal oxide active compositions of the
general formula I, the volume-specific activity thereof can be
adjusted to the desired level. Frequently, the stoichiometric
coefficient of X.sup.6 in the inventive catalytically active
multimetal oxide compositions of the general formula I (or general
formula II or general formula III) is 0 to 15 or 0 to 8. The
catalytically active multimetal oxide compositions of the general
formula I (or general formula II or general formula III) to be used
in accordance with the invention preferably do not comprise any
element X.sup.6. This statement also applies correspondingly to the
elemental constituents X.sup.4 and X.sup.5, which have a moderating
influence on the catalytic activity. Frequently, the sum of the
stoichiometric coefficients e and f in the catalytically active
multimetal oxide compositions of the general formula I (or general
formula II or general formula III) to be employed in accordance
with the invention will be 0 to 2, or 0 to 1, or 0 to 0.2.
Of course, in a multimetal oxide composition (II) or (III) too, at
least 50 mol % of the total molar amount of elements X.sup.1
present in each must be accounted for by the element W.
Preferably in accordance with the invention, in a multimetal oxide
composition (II) or (III) too, at least 60 mol %, more preferably
at least 70 mol %, even more preferably at least 80 mol %, or at
least 90 mol %, and at best at least 95 mol % or 100 mol %, of the
total molar amount of elements X.sup.1 present in the multimetal
oxide composition (II) or (III) is accounted for by the element
W.
The hydrothermal preparation of multimetal oxide precursor
compositions is familiar to those skilled in the art (cf., for
example, Applied Catalysis A: 194 to 195 (2000), page 479 to 485;
Kinetics and Catalysis, vol. 40, No. 3, 1999, page 401 to 404;
Chem. Commun., 1999, page 517 to 518; JP-A 6/227819, JP-A
2000/26123 and DE 10033121 A1).
In particular (especially in this document), this is understood to
mean the thermal treatment of a preferably intimate mixture of
sources of the desired multimetal oxide composition I (or II or
III) in the presence of water in a pressure vessel (autoclave) at
temperatures in the range of >100.degree. C. to 600.degree. C.
(preferably .gtoreq.110.degree. C. to 400.degree. C. and more
preferably .gtoreq.130.degree. C. to 300.degree. C.) to form steam
at superatmospheric pressure. The pressure range of the working
pressure (or steam pressure) which exists in the autoclave (in the
gas phase) extends typically (from, for example, .gtoreq.200 kPa or
from .gtoreq.500 kPa) to up to 50 MPa, preferably to up to 25 MPa
or up to 22 MPa and more preferably up to 15 MPa (0.1013 MPa=1
atm). A possible representative working pressure (or steam
pressure) is 2.5 MPa. It will be appreciated that it is also
possible in accordance with the invention to employ temperatures
above 600.degree. C. and working pressures (or steam pressures)
above 50 MPa, but this is less appropriate in application terms.
Advantageously, the gas atmosphere in the autoclave during the
hydrothermal treatment consists to an extent of at least 30% by
volume, preferably to an extent of at least 50% by volume, more
preferably to an extent of at least 75% by volume and even more
preferably to an extent of at least 90% by volume, or to an extent
of at least 95% by volume, or to an extent of at least 99% by
volume, or exclusively of steam. Possible further constituents of
the gas atmosphere present in the autoclave during the hydrothermal
treatment include, for example, inert gases such as molecular
nitrogen and noble gases (e.g. Ar, He). It will be appreciated,
however, that molecular oxygen may also be a constituent of the
aforementioned gas atmosphere. Further possible constituents of the
gas atmosphere present during the hydrothermal treatment in the
autoclave are gaseous decomposition products, for example ammonia,
which can form in the course of a thermal decomposition of
corresponding sources (for example comprising ammonium ions) used
as part of the desired multimetal oxide composition I (or II or
III).
Particularly advantageously, the inventive hydrothermal treatment
is effected under those conditions under which steam and liquid
water coexist (in the autoclave, in the pressure vessel). This is
possible within the temperature range from >100.degree. C. to
374.15.degree. C. (critical temperature of water) with employment
of the appropriate pressures.
The amounts of water are appropriately such that the liquid phase,
during the hydrothermal treatment, is capable of absorbing the
total amount of the starting compounds (sources) in suspension
and/or solution (the latter being preferable in accordance with the
invention over the suspension) (preferably also based on 25.degree.
C. and 101.3 kPa).
However, also possible in accordance with the invention is a
hydrothermal procedure in which the (preferably intimate) mixture
of the starting compounds fully takes up (absorbs) any amount of
liquid water present at equilibrium in the course of hydrothermal
treatment with the steam.
Advantageously in accordance with the invention, the hydrothermal
treatment is effected at autoclave temperatures of >100.degree.
C. to 300.degree. C., preferably at temperatures of 150.degree. C.
to 250.degree. C. and more preferably at 160.degree. C. to
190.degree. C. (for example at 175.degree. C.).
Based on the total amount of water and sources of the elemental
constituents of the desired multimetal oxide composition I (or II
or III) present in the autoclave (in the pressure vessel) during
the hydrothermal treatment, the proportion by weight of the total
amount of the latter in the autoclave, in accordance with the
invention, is generally at least 1% by weight. Typically, the
aforementioned proportion by weight is not above 90% by weight.
Typically, corresponding proportions by weight are from 3 to 60% by
weight, or from 5 to 30% by weight, frequently from 5 to 15% by
weight. If one of the sources used (starting compounds) comprises,
for example, hydrate water, this is not counted with the proportion
by weight of the sources but with the proportion by weight of the
water. In other words, the above proportion by weight of the total
amount of starting compounds (sources) present in the autoclave is
calculated "water-free".
As well as water and the sources of the elemental constituents
other than oxygen in the desired multimetal oxide composition I (or
II or III), the aqueous mixture to be treated hydrothermally in the
autoclave (pressure vessel) (the aqueous mixture to be treated) may
also comprise assistants, for example setting agents to adjust the
pH thereof.
Based on a temperature of 25.degree. C. and a pressure of 101.3 kPa
(=1 atm), the pH of the aqueous mixture to be treated
hydrothermally (prior to commencement of the hydrothermal
treatment), advantageously in accordance with the invention, is at
values of <7, particularly advantageously at values of .ltoreq.6
or .ltoreq.5, and very particularly advantageously at values of
.ltoreq.4 or .ltoreq.3. Normally, the aforementioned pH, however,
is at the values of .gtoreq.0. Very particularly advantageously in
accordance with the invention, the aforementioned pH is .gtoreq.1
and .ltoreq.3, or .gtoreq.1.5 and .ltoreq.2.5. The pH values
reported and pH determinations conducted in this document are
based, unless explicitly stated otherwise, on a determination with
a Checker.RTM. pH electrode HI 98103 from HANNA Instruments
Deutschland GmbH, D-77694 Kehl. These have been calibrated before
each measurement with the aid of two aqueous buffer solutions, the
pH values of which under the corresponding conditions were 7.01 and
4.01 (Technical Buffer, Model TEP 7 (catalogue number 108702) and
TEP 4 (catalogue number 108700) from WTW (Wissenschaftlich
Technische Werkstatten GmbH) in D-82362 Weilheim).
Possible setting agents for establishing the aforementioned pH
include, in particular, strong organic and strong inorganic acids
(of the Bronsted type). Examples include nitric acid and sulfuric
acid. Preferably in accordance with the invention, the setting
agent used for the aforementioned pH is dilute sulfuric acid
(concentration 1 mol/l at 25.degree. C., 101.3 kPa). Generally,
strong acids favorable for the inventive purposes are those which
are decomposed to gaseous compounds at elevated temperatures.
Salts such as ammonium carbonate, ammonium acetate, ammonium
formate, ammonium nitrate, ammonium chloride or ammonium sulfate,
for example, may likewise be part of the aqueous mixture to be
treated hydrothermally. These can help to influence the ionic
strength of the liquid aqueous medium. Preference is given to those
mediators of the aforementioned ionic strength which are decomposed
to gaseous compounds under the action of elevated temperatures.
During the inventive hydrothermal treatment, the aqueous mixture
present in the pressure vessel may either be stirred or not
stirred. Preference is given in accordance with the invention to
stirring.
Useful sources for the elemental constituents of the relevant
multimetal oxide composition generally include those compounds
which are already oxides and/or those compounds which can be
converted to oxides by heating, at least in the presence of
molecular oxygen.
Starting compounds (sources) of the elemental constituents of the
multimetal oxide composition (I) especially useful for the
inventive hydrothermal preparation variant are all of those which
are capable of forming oxides and/or hydroxides in the course of
heating under elevated pressure with water. Of course, the starting
compounds used partly or exclusively for the inventive hydrothermal
treatment may also be oxides and/or hydroxides of the elemental
constituents.
Sources suitable in accordance with the invention for the element
Mo are, for example, molybdenum oxides such as molybdenum trioxide,
molybdenum halides such as molybdenum chloride, and molybdates such
as ammonium heptamolybdate (e.g. the tetrahydrate thereof).
Ammonium heptamolybdate and the hydrates thereof are Mo sources
particularly preferred in accordance with the invention.
Sources suitable in accordance with the invention for the element V
are, for example, vanadyl acetylacetonate, vanadates such as
ammonium metavanadate, vanadium oxides such as vanadium pentoxide
(V.sub.2O.sub.5), and vanadium halides and oxide halides such as
VOCl.sub.3. Appropriately in accordance with the invention, the
vanadium starting compounds also used are those which comprise the
vanadium in the +4 oxidation state. A V source particularly
preferred in accordance with the invention is vanadyl sulfate, and
hydrates thereof.
The sources used for the element W may, in accordance with the
invention, for example, be oxides of tungsten, for example
W.sub.2O.sub.3, WO.sub.2 and WO.sub.3. Further tungsten starting
compounds suitable in accordance with the invention are
tungsten(VI) chloride, tungsten carbide and tungsten(IV) sulfide.
Preferred W sources for the hydrothermal preparation process
according to the invention, however, are the tungstates thereof or
the acids derived therefrom. W sources particularly preferred for
the inventive purposes are ammonium paratungstate and ammonium
metavanadate, and hydrates thereof.
Useful sources for the elemental constituent Cu for the inventive
purposes are especially copper(II) salts such as copper(II)
sulfate, copper(II) nitrate and copper(II) acetate, and hydrates
thereof.
Sources suitable in accordance with the invention for the elements
tellurium are tellurium oxides such as tellurium dioxide, metallic
tellurium, tellurium halides such as TeCl.sub.2, but also tellurium
acids such as orthotelluric acid H.sub.6TeO.sub.6.
Advantageous antimony starting compounds are antimony halides such
as SbCl.sub.3, antimony oxides such as antimony trioxide
(Sb.sub.2O.sub.3), antimony acids such as HSb(OH).sub.6, but also
antimony oxide salts such as antimony oxide sulfate
[(SbO.sub.2)SO.sub.4].
Niobium sources suitable in accordance with the invention are, for
example, niobium oxides such as niobium pentoxide
(Nb.sub.2O.sub.5), niobium oxide halides such as NbOCl.sub.3,
niobium halides such as NbCl.sub.5, but also complex compounds of
niobium and organic carboxylic acids and/or dicarboxylic acids, for
example oxalates and alkoxides.
With regard to the other possible elemental constituents of a
multimetal oxide I (or II or III), useful starting compounds
suitable in accordance with the invention with regards to the
relevant hydrothermal treatment are in particular the halides,
nitrates, formates, oxalates, acetates, carbonates and/or
hydroxides thereof. Starting compounds suitable in accordance with
the invention are also oxo compounds of these elemental
constituents, for example the metalates thereof or the acids
derived therefrom, or ammonium salts derived from these acids.
It will be appreciated that useful sources of the elemental
constituents also include, for example, mixed oxides (or other
mixed salts) which comprise more than one elemental constituent and
may themselves have been obtained by a hydrothermal route.
In principle, useful sources also include multimetal oxides of the
general stoichiometry I (or II or III) which have been obtained in
a manner known per se (i.e. conventionally) by the known prior art
preparation processes (for example as described in documents DE
102010023312 A1 and EP 714700 A2, and the prior art documents
acknowledged in these two documents). As already detailed at the
outset of this document, the starting materials are sources
(starting compounds) of the elemental constituents other than
oxygen in the desired multimetal oxide active composition in the
respective stoichiometric ratio desired in the multimetal oxide
active composition, and these are used to obtain a very intimate,
preferably finely divided, dry mixture which is subsequently
converted to an active oxide by non-hydrothermal thermal treatment.
The sources may either already be oxides or those compounds which
can be converted to oxides by heating, at least in the presence of
oxygen.
The source used for the process according to the invention may also
be a conventionally produced multimetal oxide of the general
stoichiometry I (or II or III) which has already been used for
catalysis of a heterogeneously catalyzed gas phase partial
oxidation of (meth)acrolein to (meth)acrylic acid and has been
deactivated in long-term operation thereof (cf. WO 2005/047226 A1).
In this case, the employment of the process according to the
invention generally brings about regeneration (reactivation) of the
deactivated multimetal oxide composition. It will be appreciated
that this may also be applied as an active composition shell on the
surface of an inert molding (and form an eggshell catalyst together
therewith).
The inventive hydrothermal treatment generally lasts for a period
of a few minutes or hours up to a few days. A typical period is
from 0.5 h to 100 h, frequently from 5 h to 80 h or from 10 h to 50
h or from 20 h to 50 h.
Appropriately in application terms, the autoclave to be used for
the hydrothermal treatment is lined on the inside with Teflon.RTM.
(coated with Teflon (=polytetrafluorethylene)). In this way,
contamination of the aqueous mixture to be treated hydrothermally
with the pressure-resistant steel from which the pressure vessel is
otherwise normally manufactured is reliably ruled out.
Prior to the inventive hydrothermal treatment, the autoclave,
optionally including the aqueous mixture present, can be evacuated.
Subsequently, it can be filled with inert gas (N.sub.2, noble gas
(e.g. Ar)) before the temperature is increased. The two measures
can also be omitted (the latter is generally less advantageous
particularly for the long-term stability of the autoclave). Of
course, the aqueous mixture to be treated hydrothermally, prior to
commencement of the hydrothermal treatment, can additionally or
alternatively be purged with inert gas.
Appropriately in application terms, the aforementioned inert gases
can also be utilized for establishment of superatmospheric pressure
even prior to commencement of the actual hydrothermal treatment in
the autoclave.
After the hydrothermal treatment has ended, the autoclave can be
quenched to room temperature (typically 25.degree. C.) or brought
gradually to room temperature, i.e. over a prolonged period (for
example of its own accord).
Preferably, after a cooling as described above, the autoclave can
be opened and the solids which have newly formed in the course of
the hydrothermal treatment can be removed from the remaining
contents of the pressure vessel. In a simple manner, the removal
can be effected, for example, by filtration or another mechanical
separating operation (for example centrifugation).
The solids removed constitute a precursor composition for the
desired catalytically active multimetal oxide I (or II or III). In
favorable cases, this precursor composition may already display the
desired catalytic activity.
Normally, the precursor composition removed, however, is
additionally treated thermally before it finds use as a
catalytically active multimetal oxide composition I (or II or III)
for a process for heterogeneously catalyzed gas phase partial
oxidation of (meth)acrolein to (meth)acrylic acid.
The starting stoichiometry of the aqueous mixture of sources of the
relevant elemental constituents which is to be treated
hydrothermally in each case in accordance with the invention and
the stoichiometry of the resulting precursor composition need not
necessarily correspond entirely. In general, however, they will be
similar. The corresponding relationship between the two can be
determined in a few preliminary tests in each case.
In principle, in the process according to the invention, the
thermal treatment employed for the precursor composition may also
be the heterogeneously catalyzed gas phase partial oxidation of
(meth)acrolein to (meth)acrylic acid itself. In this case, the
thermal treatment is effectively effected at reaction temperature
and under (standing or flowing) reaction gas mixture as the
calcination atmosphere. The transition to the catalytically active
multimetal oxide composition is effected in this case effectively
as a prolonged formatting. If the source used for the process
according to the invention is a conventionally prepared multimetal
oxide of the general stoichiometry I (or II or III), it is
generally sufficient to employ drying of the precursor composition
obtained as the thermal treatment, the temperatures typically being
in the range from 100 to 200.degree. C. or 100 to 150.degree.
C.
Typically, the thermal treatment of the precursor composition is
effected, however, at temperatures above that temperature which has
been employed in the course of hydrothermal treatment.
Apart from the warmup phase of the precursor composition to the
required temperatures, the thermal treatment (the calcination) of
the precursor composition is effected in a manner appropriate in
accordance with the invention at a temperature of 300 to
700.degree. C., frequently at a temperature of 350 to 650.degree.
C., or 400 to 600.degree. C. The thermal treatment can be effected
either under reduced pressure or under a gaseous atmosphere. It can
be conducted under an oxidizing, reducing and/or inert gas
atmosphere. A useful oxidizing gas atmosphere for the thermal
treatment of the precursor composition is, for example, air,
molecular oxygen-enriched air or molecular oxygen-depleted air (it
will be appreciated that any other mixture of molecular oxygen and
an inert gas can also be employed as an oxidizing gas atmosphere).
Preferably, the thermal treatment of the precursor composition, in
accordance with the invention, is conducted under an inert
atmosphere, i.e., for example, under molecular nitrogen and/or
noble gas. "Inert" means that the content in the gas atmosphere of
O.sub.2 and reducing constituents is in each case .ltoreq.3% by
volume, better .ltoreq.1% by volume, even better .ltoreq.0.1% by
volume and at best 0% by volume.
When the thermal treatment of the precursor composition is effected
under gaseous atmosphere, this may either be stationary or flowing.
Overall, the thermal treatment of the precursor composition may
last for up to 24 h or more. Frequently, the thermal treatment of
the precursor composition extends to a period of 0.5 h to 10 h, or
of 1 h to 5 h. Elevated temperatures are normally associated with
shorter durations of thermal treatment and, at lower temperatures,
generally longer periods of thermal treatment are employed. High
temperatures and long treatment times generally reduce the specific
surface area of the catalytically active multimetal oxide
composition I (or II or III) which results in the course of thermal
treatment of the precursor composition.
The removal of the precursor composition after the hydrothermal
treatment of the corresponding aqueous mixture has ended from the
remaining contents of the pressure vessel may comprise, in addition
to, for example, a mechanical separating operation (for example
filtration), also a washing operation on the precursor composition
which has been removed, for example, by mechanical means with a
(suitable) liquid. In the course of such a washing operation,
residual starting constituents (or setting agent used to adjust the
pH) which still remain adhering on the surfaces of the precursor
composition from the hydrothermal treatment, and/or by-products
formed, can be removed advantageously in accordance with the
invention.
Useful washing liquids of this kind include, for example, water,
organic acids or aqueous solutions thereof (e.g. oxalic acid,
formic acid, acetic acid and tartaric acid) and inorganic acids and
aqueous solutions thereof (e.g. sulfuric acid, perchloric acid,
hydrochloric acid, nitric acid and/or telluric acid), but also
alcohols, alcoholic solutions of the aforementioned acids or
hydrogen peroxide and aqueous solutions thereof.
It will be appreciated that mixtures of the aforementioned wash
liquids can also be used for washing. Preferably in accordance with
the invention, the wash liquid used is a solution of oxalic acid in
water. A suitable oxalic acid content of such a solution may, for
example, be 0.4 mol of oxalic acid/I of solution (at 25.degree. C.
and 101.3 kPa). Advantageously in accordance with the invention,
the washing is effected at an elevated temperature (e.g. 70 to
80.degree. C.). Appropriately in accordance with the invention,
this is followed by washing with water.
The washing may be followed, after the removal of the wash liquid,
by the thermal treatment of the precursor composition to be
performed as already described.
For the sake of good order, it should be stated at this point that
the thermal treatment of the precursor composition can also be
commenced initially under oxidizing (molecular oxygen comprising)
atmosphere (e.g. under air) and then continued under inert gas
atmosphere (or vice versa) etc.
It will be appreciated that the precursor composition, prior to
thermal treatment thereof, can also be comminuted to powder or
spall.
The catalytically active multimetal oxide compositions I (or II or
III) obtainable in accordance with the invention can be used as
such (for example comminuted to powder or to spall) or else shaped
to shaped bodies as catalytic active compositions for the
heterogeneously catalyzed partial gas phase oxidation of
(meth)acrolein to (meth)acrylic acid. The catalyst bed may be a
fixed bed, a moving bed or a fluidized bed.
In the case of unsupported catalysts, the shaping can be effected,
for example, by extrusion or tabletting, and, in the case of
eggshell catalysts, by application to a support body, as described
in DE 10118814 A1, or PCT/EP/02/04073, or DE 10051419 A1, or DE
102010023312 A1, or DE 102007010422 A1, or EP 714700 A2.
The support bodies to be used for the multimetal oxide compositions
I (or II or III) obtainable in accordance with the invention in the
case of eggshell catalysts are preferably chemically inert. In
other words, they essentially do not intervene in the course of the
heterogeneously catalyzed partial gas phase oxidation of
(meth)acrolein to (meth)acrylic acid.
Useful materials for the support bodies include, in accordance with
the invention, especially aluminum oxide, silicon dioxide,
silicates such as clay, kaolin, steatite (preferably C-220 steatite
from CeramTec (DE), or preferably with a low water-soluble alkali
content), pumice, aluminum silicate, magnesium silicate, silicon
carbide and zirconium dioxide.
The surface of the support body may be either smooth or rough.
Advantageously, the surface of the support body is rough, since an
elevated surface roughness generally causes increased adhesive
strength of the active composition shell applied.
Useful support bodies with distinct surface roughness include
especially support bodies which have a grit layer on their
surface.
The surface roughness R.sub.z, of the support body is preferably in
the range from 30 to 100 .mu.m, more preferably in the range from
50 to 70 .mu.m (determined to DIN 4768 sheet 1 with a "Hommel
Tester for DIN ISO surface parameters" from Hornmelwerke).
Particular preference is given to rough-surface support bodies from
CeramTec made from C220 steatite.
The support materials may be porous or nonporous. The support
material is preferably nonporous (the total volume of the pores
based on the volume of the support body is advantageously
.ltoreq.1% by volume).
The support bodies may be regular or irregular in shape, preference
being given to support bodies of regular shape.
The longest dimension of the support bodies is normally in the
range from 1 to 10 mm (the longest dimension is the longest direct
straight line connecting two points on the surface of a support
body).
Preference is given in accordance with the invention to spheres or
cylinders, especially hollow cylinders (rings), as support bodies.
Favorable diameters for support spheres are 1 to 4 mm. If cylinders
are used as support bodies, the length thereof is preferably 2 to
10 mm and the external diameter thereof preferably 4 to 10 mm. In
the case of rings, the wall thickness is additionally typically 1
to 4 mm. Annular support bodies suitable in accordance with the
invention may also have a length of 3 to 6 mm, an external diameter
of 4 to 8 mm and a wall thickness of 1 to 2 mm. Also possible,
however, is a support ring geometry of 7 mm.times.3 mm.times.4 mm,
or of 5 mm.times.3 mm.times.2 mm (external
diameter.times.length.times.internal diameter).
The thickness of the active multimetal oxide composition shell on
the surface of the support bodies of inventive eggshell catalysts
is typically 10 to 1000 .mu.m. It may also be 50 to 700 .mu.m, 100
to 600 .mu.m or 150 to 500 .mu.m. Possible shell thicknesses are
also 10 to 500 .mu.m, 100 to 500 .mu.m or 150 to 300 .mu.m.
Inventive eggshell catalysts can be produced in the simplest manner
by preforming the desired multimetal oxide composition of the
general formula I, converting it to a finely divided form and
finally applying it to the surface of the support body with the aid
of a liquid binder.
For this purpose, the surface of the support body is appropriately
moistened in a controlled manner with the liquid binder (for
example by spraying) and a layer of the active composition is fixed
on the moistened surface by contacting the support bodies thus
moistened with finely divided catalytically active multimetal oxide
I (or II or III) obtained in accordance with the invention (for
example, dust the moistened support bodies with active composition
powder as described in EP 714700 A2). Subsequently, the coated
support bodies are dried and the adhesion liquid is at least partly
removed (for example by passing hot gas through; cf. WO
2006/094766). "Moisten in a controlled manner" means in this
context that the support surface is appropriately moistened in such
a way that it has adsorbed liquid binder but no liquid phase as
such is visible on the support surface. If the support surface is
too moist, the finely divided, catalytically active multimetal
oxide composition agglomerates to form separate agglomerates rather
than attaching to the surface. Detailed information on this subject
can be found in DE 2909671 A1 and in DE 10051419 A1. Of course, the
operation can be repeated periodically to achieve an increased
layer thickness. In this case, the coated base body becomes the new
"support body" etc. However, it is also possible to employ all
other application processes acknowledged as prior art in EP 714700
A2 for preparation of inventive eggshell catalysts. In principle,
inventive eggshell catalysts can be also be produced by first
applying finely divided precursor composition to the surface of the
support body and performing the thermal treatment of the precursor
composition to give the catalytically active multimetal oxide
composition of the general formula I (or II or III) only
subsequently, i.e. with it already present on the surface of the
support body.
Examples of useful liquid binders include water, an organic solvent
or a solution of an organic substance (for example of an organic
solvent) in water or in an organic solvent. Examples of organic
binders include mono- or polyhydric organic alcohols, for example
ethylene glycol, 1,4-butanediol, 1,6-hexanediol or glycerol, mono-
or polybasic organic carboxylic acids such as propionic acid,
oxalic acid, malonic acid, glutaric acid or maleic acid, amino
alcohols such as ethanolamine or diethanolamine, and mono- or
polyfunctional organic amides such as formamide. Suitable organic
binder promoters soluble in water, in an organic liquid or in a
mixture of water and an organic liquid are, for example,
monosaccharides and oligosaccharides such as glucose, fructose,
sucrose and/or lactose.
Particularly advantageously, the liquid binder used is a solution
consisting of 20 to 90% by weight of water and 10 to 80% by weight
of an organic compound. The organic component in the aforementioned
liquid binders is preferably 10 to 50% and more preferably 20 to
30% by weight. Very particularly preferred liquid binders are
solutions consisting of 20 to 90% by weight of water and 10 to 80%
by weight of glycerol. Advantageously, the glycerol component in
these aqueous solutions is 10 to 50% by weight and more preferably
20 to 30% by weight. One reason for the advantage of binders
preferred in accordance with the invention is that they are capable
of wetting both the finely divided active composition (or the
finely divided precursor composition) and the support bodies in an
entirely satisfactory manner.
The fineness of the catalytically active multimetal oxide
composition of the general formula I (or II or III) to be applied
to the surface of the support body, or of the precursor composition
thereof, is of course matched to the desired layer thickness.
Suitable active composition powders for the shell thickness range
from 100 to 500 .mu.m are, for example, those of which at least 50%
of the total number of powder particles pass through the mesh size
of 1 to 20 .mu.m or alternatively 1 to 10 .mu.m and where the
numerical proportion of particles having a longest dimension above
50 .mu.m is less than 10%. For the rest, the statements made on
page 18 of WO 2005/120702 A1 apply correspondingly.
Preferably in accordance with the invention, inventive eggshell
catalysts will be produced by the mode of preparation described and
executed by way of example in EP 714700 A2. An aqueous solution of
75% by weight of water and 25% by weight of glycerol is the
preferred binder. The process for thermal treatment of the
precursor composition will, advantageously in accordance with the
invention, be conducted by the procedure described and executed by
way of example in DE 10360057 A1.
In order to additionally increase the long-term stability of an
inventive eggshell catalyst, following the teaching of US
2008/214863 A1, rather than solely finely divided multimetal oxide
composition I (or II or III), it is advantageously possible to
apply to the surface of the support body a finely divided mixture
thereof with a finely divided substance S from the group consisting
of oxides of molybdenum and of compounds of molybdenum from which
an oxide of molybdenum is formed under the action of elevated
temperature and molecular oxygen.
Remarkably, multimetal oxide compositions of the general formula I
(or II or III) prepared in accordance with the invention are
characterized by an elevated specific surface area SA (BET surface
area, molecular nitrogen).
In general, SA .gtoreq.15 m.sup.2/g or .gtoreq.20 m.sup.2/g; in
many cases, SA is at values of .gtoreq.25 m.sup.2/g, or at values
of .gtoreq.30 m.sup.2/g. Normally, SA will not exceed 150
m.sup.2/g. In some cases, the values achieved for SA are
.ltoreq.100 m.sup.2/g, or .ltoreq.60 m.sup.2/g or .ltoreq.50
m.sup.2/g or .ltoreq.40 m.sup.2/g. Particularly high values for SA
are obtained when a conventionally prepared multimetal oxide of the
general stoichiometry I (or II or III) as the source in the process
according to the invention is "hydrothermally after treated".
To determine specific surface areas SA, sample weights of about 1 g
were used. The determinations themselves were effected with an
AUTOSORB 3B instrument from Quantachrome GmbH & Co. KG in
DE-85235 Odelzhausen. To prepare for the actual measurement, the
sample to be analyzed in each case was first held under high vacuum
at 200.degree. C. for 10 h and then purged with helium at
200.degree. C. over 24 h. This was followed by the nitrogen
adsorption at -196.degree. C.
In general, multimetal oxide compositions of the general formula I
(or II or III) prepared in accordance with the invention have not
an X-ray-amorphous but a semicrystalline structure (i.e. the X-ray
diffractogram has only few (generally fewer than 5) separate
diffraction lines (reflections) whose half-height width on the 2
theta scale is .ltoreq.4.degree. (the half-height width is as
defined in DE 10321398 A1)) (in this document, figures given for
X-ray diffractograms relate in each case to a powder diffractogram
using Cu--K.sub..alpha.1 radiation (.lamda.=1.540698 .ANG.); the
diffractometer used was a Stadi P instrument from Stoe & Cie
GmbH in D-64295 Darmstadt, which monochromatized the radiation used
with a Ge [1,1,1] single crystal; the radiation reflected by the
sample was recorded with a location-sensitive detector (Mythen 1K
detector from Dectris Ltd. in CH-5400 Baden)). The assignment of a
crystal structure is normally impossible.
The catalytically active multimetal oxide compositions of the
general formula I (or II or III) obtainable in accordance with the
invention, and catalysts equipped (modified) therewith or shaped
therefrom, are especially suitable as catalysts for a process for
heterogeneously catalyzed partial gas phase oxidation of
(meth)acrolein to (meth)acrylic acid, and more preferably for a
process for heterogeneously catalyzed partial gas phase oxidation
of acrolein to acrylic acid. They are notable particularly in that
a catalyst bed charged therewith, in the course of performance of
the partial oxidation, has a high service life over which the
target product is formed at high activity with high
selectivity.
This is particularly true when the heterogeneously catalyzed
partial gas phase oxidation of (meth)acrolein to (meth)acrylic acid
is performed at high (meth)acrolein loads, as described, for
example, by DE 10307983 A1, DE 19948523 A1 and DE 19910508 A1.
The heterogeneously catalyzed partial gas phase oxidation can be
performed in a manner known per se. In other words, a reaction gas
mixture comprising the (meth)acrolein, molecular oxygen and at
least one inert diluent gas is conducted at elevated temperature
through a catalyst bed whose catalysts have, as the active
composition, at least one multimetal oxide composition of the
general formula I (or II or III) and, during the residence time of
the (meth)acrolein in the catalyst bed, it is converted to
(meth)acrylic acid. A catalyst bed preferred in accordance with the
invention is a fixed catalyst bed. In principle, for the process
according to the invention, however, a fluidized bed or a moving
bed are also useful. In general, steam as a constituent of the
reaction gas mixture leads to an improvement in selectivity and
activity.
Otherwise, inert diluent gases with elevated molar specific heat,
for example n-propane or CO.sub.2, are advantageous.
Particularly suitable for performance of the gas phase partial
oxidation of (meth)acrolein are heat exchanger reactors. A heat
exchanger reactor has at least one primary space and at least one
secondary space, the two being divided from one another by a
dividing wall. In the at least one primary space is positioned the
catalyst charge which comprises at least one multimetal oxide
composition of the general formula I (or II or III), through which
a reaction gas mixture comprising (meth)acrolein flows. At the same
time, a fluid heat carrier flows through the secondary space and
the heat exchange takes place between the two spaces through the
dividing wall, this pursuing the purpose of controlling the
temperature of the reaction gas mixture on the route thereof
through the catalyst bed.
In general, the gas phase partial oxidation of (meth)acrolein is
conducted in a shell-and-tube (heat exchanger) reactor having one
or more temperature zones, as described, for example, by EP 700714
A1, EP 700893 A1, DE 19910508 A1, DE 19948523 A1, DE 19910506 A1,
DE 19948241 A1, DE 2830765 A1, DE 2513405 A1, U.S. Pat. No.
3,147,084 A, DE 2201528 A1, EP 383224 A2, JP 2007-260588 A and JP
58096041 A.
A fixed catalyst bed is present here in the form of a corresponding
bed of shaped catalyst bodies (optionally in a mixture with
diluting inert shaped bodies) in the metal tubes (catalyst tubes)
of the tube bundle reactor, and the temperature medium/media is/are
conducted around the metal tubes (in the case of more than one
temperature zone, a corresponding number of essentially spatially
separate temperature media are conducted around the metal tubes).
The temperature medium is generally a salt melt. The reaction gas
mixture is conducted through the catalyst tubes.
Alternatively, the fixed catalyst bed may, for example, also be
present in the spaces between thermoplates of a thermoplate reactor
through which a heat carrier flows, as recommended, for example, by
DE 102004017150 A1, DE 19952964 A1 and DE 10361456 A1.
The fixed catalyst bed may, as already stated, quite generally
consist only of catalysts obtainable in accordance with the
invention, but also of such catalysts diluted with inert shaped
bodies. The inert shaped bodies used may, for example, be the
shaped support bodies (support bodies) used for preparation of
inventive eggshell catalysts. Upstream of and/or beyond the fixed
catalyst bed may be a pure inert shaped body bed (such pure inert
shaped body beds are not normally included in the calculation of
the space velocity on the fixed catalyst bed with reaction gas or
with a reaction gas component).
Catalyst tubes used in a shell-and-tube reactor are customarily
manufactured from ferrite steel and typically have a wall thickness
of 1 to 3 mm. The internal diameter thereof is generally 20 to 30
mm, frequently 21 to 26 mm. The length thereof is appropriately 2
to 4 m.
Appropriately in application terms, the number of catalyst tubes
accommodated in the shell-and-tube vessel runs to at least 5000,
preferably to at least 10 000. Frequently, the number of catalyst
tubes accommodated in the reactor vessel is 15 000 to 40 000.
Shell-and-tube reactors having a number of catalyst tubes above 50
000 are usually exceptional. Within the vessel, the catalyst tubes
are normally arranged in homogeneous distribution (preferably 6
equidistant neighboring tubes per catalyst tube), and the
distribution is appropriately selected such that the distance
between the central internal axes of mutually closest catalyst
tubes (called the catalyst tube pitch) is 35 to 45 mm (cf., for
example, EP-B 468290 A1).
The heat exchange media used for shell-and-tube reactors are
particularly favorably melts of salts such as potassium nitrate,
potassium nitrite, sodium nitrite and/or sodium nitrate, or of
low-melting metals such as sodium, mercury and alloys of various
metals.
Charging of catalyst tubes in shell-and-tube reactors with
catalysts obtainable in accordance with the invention is
advantageous particularly when the shell-and-tube reactor is
operated at a (meth)acrolein space velocity on the catalyst charge
which is .gtoreq.135 l (STP)/lh, or .gtoreq.150 l (STP)/lh, or
.gtoreq.160 l (STP)/lh, or .gtoreq.170 l (STP)/lh, or .gtoreq.180 l
(STP)/lh, or .gtoreq.200 l (STP)/lh, or .gtoreq.220 l (STP)/lh, or
.gtoreq.240 l (STP)/lh. Of course, such a catalyst charge is also
advantageous at lower (e.g. .ltoreq.130 l (STP)/lh, or .ltoreq.100
l (STP)/lh, or .ltoreq.80 l (STP)/lh, or .ltoreq.60 l (STP)/lh)
(meth)acrolein space velocities.
In general, the (meth)acrolein space velocity on the catalyst
charge will, however, be .ltoreq.350 l (STP)/lh, or .ltoreq.300 l
(STP)/lh, or .ltoreq.250 l (STP)/lh (corresponding space velocities
can also be implemented in thermoplate reactors).
The terms "space velocity" and "l (STP)" are used as defined in DE
19927624 A1.
The volume-specific activity of the fixed catalyst bed will
generally be configured such that it increases in flow direction of
the reaction gas.
This can be implemented in a simple manner, for example, by
decreasing the dilution level of the fixed catalyst bed with inert
shaped bodies in flow direction of the reaction gas.
Otherwise, the heterogeneously catalyzed partial oxidation with,
for example, eggshell catalysts obtainable in accordance with the
invention can quite generally be performed in all aspects as
detailed, for example, by DE A 10350822 A1. The (meth)acrolein
content in the reaction gas input mixture may, for example, be at
values of 3 or 6 to 15% by volume, frequently 4 or 6 to 10% by
volume, or 5 to 8% by volume (based in each case on the total
volume).
The molar ratio of O.sub.2:(meth)acrolein in the reaction gas input
mixture will normally be .gtoreq.1. This ratio will typically be at
values of .ltoreq.3. In many cases, the heterogeneously catalyzed
(meth)acrolein partial oxidation to (meth)acrylic acid will be
executed with a (meth)acrolein oxygen:steam:inert gas volume ratio
(l(STP)) present in the reaction gas input mixture of 1:(1 to 3):(0
to 20):(3 to 30), preferably of 1:(1 to 3):(0.5 to 10):(7 to
10).
Useful inert diluent gases (these are gases or mixtures of such
gases which, on single pass of the reaction gas mixture through the
catalyst bed (e.g. fixed bed), remain chemically unchanged to an
extent of at least 95 mol %, preferably to an extent of at least 97
mol % or to an extent of at least 99 mol %, and at best to an
extent of 100 mol %) include N.sub.2, CO.sub.2, CO, noble gases,
propane, ethane, methane, butane and/or pentane (i.e. each as the
sole diluent gas or in a mixture with another inert diluent gas or
with several others among these inert diluent gases). The reaction
temperatures of such a heterogeneously catalyzed (meth)acrolein
partial oxidation are typically in the range from 200 to
400.degree. C., generally from 220 to 380.degree. C., in many cases
from 230 to 350.degree. C., frequently from 245 to 285.degree. C.,
or from 245 to 265.degree. C. The working pressure is normally
101.3 to 350 kPa.
The (meth)acrolein conversion, based on a single pass of the
reaction gas mixture through the, for example, fixed catalyst bed,
is typically .gtoreq.90 mol %, or .gtoreq.96 mol %, frequently
.gtoreq.98 mol %, and in many cases .gtoreq.99 mol %.
For the rest, the inventive partial oxidation process can be
executed in a manner entirely corresponding to the recommendations
and teachings of DE 102007019597 A1.
More particularly, the source used for the (meth)acrolein required
for the inventive partial oxidation may directly be the
(meth)acrolein-comprising product gas mixture from a
heterogeneously catalyzed partial oxidation of a C.sub.3/C.sub.4
precursor compound (e.g. propene or isobutene) of (meth)acrolein to
(meth)acrolein, without any need to remove the (meth)acrolein from
such a product gas mixture beforehand.
The selectivity S of (meth)acrylic acid formation (mol %) is
understood in this document to mean:
.times..times..times..times..times..times..times..times..times..times..ti-
mes..times..times..times..times..times..times..times..times..times..times.-
.times..times..times..times..times..times..times..times..times..times..tim-
es..times. ##EQU00001## (the conversions are each based on a single
pass of the reaction gas mixture through the catalyst bed).
An active composition (catalyst) which leads to the same conversion
at lower temperature under otherwise unchanged reaction conditions
has a higher activity.
The conversion C of (meth)acrolein (mol %) is defined in a
corresponding manner as:
.times..times..times..times..times..times..times..times..times..times..ti-
mes..times..times..times..times..times..times..times..times..times..times.-
.times..times..times..times..times..times. ##EQU00002##
The (meth)acrylic acid can be removed from the product gas mixture
of the partial oxidation in a manner known per se, for example by
first converting the (meth)acrylic acid to the condensed phase by
absorptive and/or condensative measures. Subsequent thermal
separation processes, for example rectification and/or
crystallization, can subsequently isolate (meth)acrylic acid from
the condensed phase in any desired purity (cf., for example, DE
602004924 T2 and WO 2006/114428 A1, and the prior art cited in
these documents).
Thus, the present application comprises especially the following
inventive embodiments: 1. A process for heterogeneously catalyzed
gas phase partial oxidation of (meth)acrolein to (meth)acrylic acid
over a catalytically active multimetal oxide composition of the
general formula I
Mo.sub.12V.sub.aX.sup.1.sub.bX.sup.2.sub.cX.sup.3.sub.dX.sup.4.sub.eX.s-
up.5.sub.fX.sup.6.sub.gO.sub.n (I) in which the variables are each
defined as follows: X.sup.1=W, Nb, Ta, Cr and/or Ce, X.sup.2=Cu,
Ni, Co, Fe, Mn and/or Zn, X.sup.3=Sb, Te and/or Bi, X.sup.4=one or
more alkali metals (Li, Na, K, Rb and/or Cs) and/or H, X.sup.5=one
or more alkaline earth metals (Mg, Ca, Sr and/or Ba), X.sup.6=Si,
Al, Ti and/or Zr, a=1 to 6, b=0.2 to 8, c=0 to 18, d=0 to 40, e=0
to 4, f=0 to 4, g=0 to 40, and n=a number which is determined by
the valency and frequency of the elements in I other than oxygen,
wherein at least 50 mol % of the total molar amount of elements
X.sup.1 present in the multimetal oxide composition (I) is
accounted for by the element W, and the multimetal oxide
composition (I) is prepared by a process in which a mixture of
sources of the elemental constituents of the multimetal oxide
composition (I) is subjected to a hydrothermal treatment in the
presence of water in a pressure vessel (as an aqueous mixture), the
newly forming solid is removed as a precursor composition and the
precursor composition is converted to the catalytically active
multimetal oxide composition (I) by thermal treatment. 2. The
process according to embodiment 1, wherein at least 60 mol % of the
total molar amount of elements X.sup.1 present in the multimetal
oxide composition (I) is accounted for by the element W. 3. The
process according to embodiment 1, wherein at least 70 mol % of the
total molar amount of elements X.sup.1 present in the multimetal
oxide composition (I) is accounted for by the element W. 4. The
process according to embodiment 1, wherein at least 80 mol % of the
total molar amount of elements X.sup.1 present in the multimetal
oxide composition (I) is accounted for by the element W. 5. The
process according to embodiment 1, wherein at least 90 mol % of the
total molar amount of elements X.sup.1 present in the multimetal
oxide composition (I) is accounted for by the element W. 6. The
process according to embodiment 1, wherein at least 95 mol % of the
total molar amount of elements X.sup.1 present in the multimetal
oxide composition (I) is accounted for by the element W. 7. The
process according to embodiment 1, wherein 100 mol % of the total
molar amount of elements X.sup.1 present in the multimetal oxide
composition (I) is accounted for by the element W. 8. The process
according to any of embodiments 1 to 7, wherein the stoichiometric
coefficient b is 0.2 to 4. 9. The process according to any of
embodiments 1 to 7, wherein the stoichiometric coefficient b is 0.2
to 3. 10. The process according to any of embodiments 1 to 9,
wherein the stoichiometric coefficient c is 0.5 to 18. 11. The
process according to any of embodiments 1 to 9, wherein the
stoichiometric coefficient c is 0.5 to 10. 12. The process
according to any of embodiments 1 to 9, wherein the stoichiometric
coefficient c is 0.5 to 3. 13. The process according to any of
embodiments 1 to 12, wherein the stoichiometric coefficient a is 1
to 5. 14. The process according to any of embodiments 1 to 13,
wherein the stoichiometric coefficient a is 2 to 4. 15. The process
according to any of embodiments 1 to 14, wherein the stoichiometric
coefficient d is 0 to 20. 16. The process according to any of
embodiments 1 to 14, wherein the stoichiometric coefficient d is 0
to 10. 17. The process according to any of embodiments 1 to 14,
wherein the stoichiometric coefficient d is 0 to 2. 18. The process
according to any of embodiments 1 to 17, wherein the stoichiometric
coefficient e is 0 to 2. 19. The process according to any of
embodiments 1 to 18, wherein the stoichiometric coefficient f is 0
to 2. 20. The process according to any of embodiments 1 to 19,
wherein X.sup.1=W, Nb and/or Cr. 21. The process according to any
of embodiments 1 to 19, wherein X.sup.1=W and Nb. 22. The process
according to any of embodiments 1 to 19, wherein X.sup.1=W. 23. The
process according to any of embodiments 1 to 22, wherein
X.sup.2=Cu, Ni, Co and/or Fe. 24. The process according to any of
embodiments 1 to 22, wherein X.sup.2=Cu and/or Ni. 25. The process
according to any of embodiments 1 to 22, wherein X.sup.2=Cu. 26.
The process according to any of embodiments 1 to 25, wherein
X.sup.3=Sb. 27. The process according to any of embodiments 1 to
26, wherein X.sup.4=Na, K and/or H. 28. The process according to
any of embodiments 1 to 27, wherein X.sup.5=Ca, Sr and/or Ba. 29.
The process according to any of embodiments 1 to 28, wherein
X.sup.6=Si, Al and/or Ti. 30. The process according to any of
embodiments 1 to 28, wherein X.sup.6=Si and/or Al. 31. The process
according to any of embodiments 1 to 7, wherein the variables of
the general formula I are each defined as follows: X.sup.1=W, Nb
and/or Cr, X.sup.2=Cu, Ni, Co and/or Fe X.sup.3=Sb, X.sup.4=Na, K
and/or H, X.sup.5=Ca, Sr and/or Ba, X.sup.6=Si, Al and/or Ti, a=1
to 5, b=0.2 to 4, c=0.5 to 18, d=0 to 10, e=0 to 2, f 32 0 to 2,
g=0 to 15, and n=a number which is determined by the valency and
frequency of the elements in the general formula I other than
oxygen. 32. The process according to embodiment 31, wherein at
least 50 mol % of the total molar amount of elements X.sup.2
present in the multimetal oxide composition (I) is accounted for by
the element Cu. 33. The process according to embodiment 31, wherein
at least 70 mol % of the total molar amount of elements X.sup.2
present in the multimetal oxide composition (I) is accounted for by
the element Cu. 34. The process according to embodiment 31, wherein
at least 90 mol % of the total molar amount of elements X.sup.2
present in the multimetal oxide composition (I) is accounted for by
the element Cu. 35. The process according to embodiment 31, wherein
100 mol % of the total molar amount of elements X.sup.2 present in
the multimetal oxide composition (I) is accounted for by the
element Cu. 36. The process according to any of embodiments 1 to 7,
wherein the catalytically active multimetal oxide composition
satisfies the general stoichiometry II
Mo.sub.12V.sub.aX.sup.1.sub.bX.sup.2.sub.cX.sup.4.sub.eX.sup.5.sub.fX.sup-
.6.sub.gO.sub.n (II) in which the variables are each defined as
follows: X.sup.1=W and/or Nb, X.sup.2=Cu and/or Ni, X.sup.4=H,
X.sup.5=Ca and/or Sr, X.sup.6=Si and/or Al, a=2 to 4, b=0.2 to 3,
c=0.5 to 3, e=0 to 2, f=0 to 0.5, g=0 to 8, and n=a number which is
determined by the valency and frequency of the elements in the
general formula II other than oxygen. 37. The process according to
embodiment 36, wherein at least 50 mol % of the total molar amount
of elements X.sup.2 present in the multimetal oxide composition is
accounted for by the element Cu. 38. The process according to
embodiment 36, wherein at least 70 mol % of the total molar amount
of elements X.sup.2 present in the multimetal oxide composition is
accounted for by the element Cu. 39. The process according to
embodiment 36, wherein at least 90 mol % of the total molar amount
of elements X.sup.2 present in the multimetal oxide composition is
accounted for by the element Cu. 40. The process according to
embodiment 36, wherein 100 mol % of the total molar amount of
elements X.sup.2 present in the multimetal oxide composition is
accounted for by the element Cu. 41. The process according to any
of embodiments 1 to 7, wherein the catalytically active multimetal
oxide composition satisfies the general stoichiometry III
Mo.sub.12V.sub.aW.sub.bCu.sub.cX.sup.4.sub.eX.sup.5.sub.fX.sup.6.sub.gO.s-
ub.n (III) in which the variables are each defined as follows:
X.sup.4=one or more alkali metals (Li, Na, K, Rb and/or Cs) and/or
H, X.sup.5=one or more alkaline earth metals (Mg, Ca, Sr and/or
Ba), X.sup.6=one or more elements from the group of Si, Al, Ti and
Zr, a=2 to 4, b=0.2 to 3, c=0.5 to 2, e=0 to 4, f=0 to 4, with the
proviso that the sum of e and f does not exceed 4, g=0 to 40, and
n=a number which is determined by the valency and frequency of the
elements in the general formula Ill other than oxygen. 42. The
process according to embodiment 41, wherein the stoichiometric
coefficient b is 0.5 to 2. 43. The process according to embodiment
41 or 42, wherein the stoichiometric coefficient a is 2.5 to 3.5.
44. The process according to any of embodiments 41 to 43, wherein
the stoichiometric coefficient c is 1 to 1.5. 45. The process
according to any of embodiments 1 to 44, wherein the hydrothermal
treatment is effected at temperatures in the range of
>100.degree. C. to 600.degree. C. 46. The process according to
any of embodiments 1 to 45, wherein the hydrothermal treatment is
effected at temperatures in the range of .gtoreq.110.degree. C. to
400.degree. C. 47. The process according to any of embodiments 1 to
46, wherein the hydrothermal treatment is effected at temperatures
in the range of .gtoreq.130.degree. C. to 300.degree. C. 48. The
process according to any of embodiments 1 to 47, wherein the
hydrothermal treatment is effected at a superatmospheric working
pressure of .ltoreq.50 MPa. 49. The process according to any of
embodiments 1 to 48, wherein the hydrothermal treatment is effected
at a working pressure of .gtoreq.200 kPa and .ltoreq.25 MPa or at a
working pressure of .gtoreq.500 kPa and .ltoreq.22 MPa. 50. The
process according to any of embodiments 1 to 49, wherein steam and
liquid water coexist during the hydrothermal treatment. 51. The
process according to any of embodiments 1 to 50, wherein the
hydrothermally treated aqueous mixture is a suspension. 52. The
process according to any of embodiments 1 to 50, wherein the
hydrothermally treated aqueous mixture is a solution. 53. The
process according to any of embodiments 1 to 52, wherein, based on
the amount of water and sources of the elemental constituents
present in the pressure vessel during the hydrothermal treatment,
the proportion by weight of the total amount of sources is at least
1% by weight. 54. The process according to any of embodiments 1 to
53, wherein, based on the amount of water and sources of the
elemental constituents present in the pressure vessel during the
hydrothermal treatment, the proportion by weight of the total
amount of sources is not more than 90% by weight. 55. The process
according to any of embodiments 1 to 54, wherein, based on the
amount of water and sources of the elemental constituents present
in the pressure vessel during the hydrothermal treatment, the
proportion by weight of the total amount of the sources is 3 to 60%
by weight. 56. The process according to any of embodiments 1 to 55,
wherein, based on the amount of water and sources of the elemental
constituents present in the pressure vessel during the hydrothermal
treatment, the proportion by weight of the total amount of the
sources is 5 to 30% by weight. 57. The process according to any of
embodiments 1 to 56, wherein, based on the amount of water and
sources of the elemental constituents present in the pressure
vessel during the hydrothermal treatment, the proportion by weight
of the total amount of the sources is 5 to 15% by weight. 58. The
process according to any of embodiments 1 to 57, wherein the
aqueous mixture subjected to the hydrothermal treatment at
25.degree. C. and 103.1 kPa has a pH of <7. 59. The process
according to any of embodiments 1 to 57, wherein the aqueous
mixture subjected to the hydrothermal treatment at 25.degree. C.
and 103.1 kPa has a pH of .ltoreq.6. 60. The process according to
any of embodiments 1 to 57, wherein the aqueous mixture subjected
to the hydrothermal treatment at 25.degree. C. and 103.1 kPa has a
pH of .ltoreq.5. 61. The process according to any of embodiments 1
to 57, wherein the aqueous mixture subjected to the hydrothermal
treatment at 25.degree. C. and 103.1 kPa has a pH of .ltoreq.4. 62.
The process according to any of embodiments 1 to 57, wherein the
aqueous mixture subjected to the hydrothermal treatment at
25.degree. C. and 103.1 kPa has a pH of .ltoreq.3. 63. The process
according to any of embodiments 1 to 62, wherein the aqueous
mixture subjected to the hydrothermal treatment at 25.degree. C.
and 103.1 kPa has a pH of .gtoreq.0. 64. The process according to
any of embodiments 1 to 63, wherein the aqueous mixture subjected
to the hydrothermal treatment at 25.degree. C. and 103.1 kPa has a
pH of .gtoreq.1 and .ltoreq.3. 65. The process according to any of
embodiments 1 to 64, wherein the aqueous mixture subjected to the
hydrothermal treatment at 25.degree. C. and 103.1 kPa has a pH of
.gtoreq.1.5 and .ltoreq.2.5. 66. The process according to any of
embodiments 58 to 65, wherein the aqueous mixture subjected to the
hydrothermal treatment comprises added sulfuric acid. 67. The
process according to any of embodiments 1 to 66, wherein the
aqueous mixture subjected to the hydrothermal treatment is stirred
during the hydrothermal treatment. 68. The process according to any
of embodiments 1 to 67, wherein at least one source of the
elemental constituent Mo is ammonium heptamolybdate and/or a
hydrate of this compound. 69. The process according to any of
embodiments 1 to 68, wherein at least one source of the elemental
constituent W is ammonium paratungstate, ammonium metatungstate
and/or a hydrate of these compounds. 70. The process according to
any of embodiments 1 to 69, wherein at least one source of the
elemental constituent vanadium comprises the vanadium in the +4
oxidation state. 71. The process according to embodiment 70,
wherein at least one source of the elemental constituent vanadium
is vanadyl sulfate and/or a hydrate of this compound. 72. The
process according to any of embodiments 1 to 71, wherein at least
one source of the elemental constituent Cu is copper(II) sulfate,
copper(II) nitrate, copper(II) acetate and/or a hydrate of these
compounds. 73. The process according to any of embodiments 1 to 72,
wherein the hydrothermal treatment takes 0.5 h to 100 h. 74. The
process according to any of embodiments 1 to 73, wherein the
hydrothermal treatment takes 5 h to 80 h. 75. The process according
to any of embodiments 1 to 74, wherein the hydrothermal treatment
is effected in the absence or presence of molecular oxygen. 76. The
process according to any of embodiments 1 to 75, wherein the
removal of the solid newly forming in the course of hydrothermal
treatment as the precursor composition comprises at least one
mechanical removal of this solid and at least one washing operation
on the mechanically removed solid with at least one wash liquid
from the group consisting of organic acids, inorganic acids and
aqueous solutions of the acids mentioned. 77. The process according
to embodiment 76, wherein the wash liquid is an aqueous solution of
oxalic acid. 78. The process according to any of embodiments 1 to
77, wherein the temperature in the course of thermal treatment of
the precursor composition is 300 to 700.degree. C. 79. The process
according to any of embodiments 1 to 78, wherein the temperature in
the course of thermal treatment of the precursor composition is 350
to 650.degree. C. 80. The process according to any of embodiments 1
to 79, wherein the temperature in the course of thermal treatment
of the precursor composition is 400 to 600.degree. C. 81. The
process according to any of embodiments 1 to 80, wherein the
thermal treatment of the precursor composition is effected under a
gas atmosphere comprising molecular oxygen. 82. The process
according to any of embodiments 1 to 80, wherein the thermal
treatment of the precursor composition is effected under reduced
pressure or under a gas atmosphere which does not comprise any
molecular oxygen. 83. The process according to any of embodiments 1
to 80, wherein the thermal treatment of the precursor composition
is effected under a reducing gas atmosphere. 84. The process
according to any of embodiments 81 to 83, wherein the thermal
treatment of the precursor composition is effected under a gas
atmosphere comprising molecular nitrogen and/or noble gas. 85. The
process according to any of embodiments 1 to 80, wherein the
thermal treatment of the precursor composition is effected under a
gas atmosphere whose content of molecular oxygen and reducing
constituents is in each case .ltoreq.3% by volume. 86. The process
according to any of embodiments 1 to 85, wherein the catalytically
active multimetal oxide composition in the heterogeneously
catalyzed partial oxidation is in a fixed bed, a moving bed or a
fluidized bed. 87. The process according to any of embodiments 1 to
86, wherein the catalytically active multimetal oxide composition
is the active composition of an eggshell catalyst in which it has
been applied to the surface of a support body. 88. The process
according to embodiment 87, wherein the catalytically active
multimetal oxide composition in the eggshell catalyst has been
applied to a spherical or annular support body. 89. The process
according to embodiment 88, wherein the catalytically active
multimetal oxide composition has been applied to the surface of the
support body using a solution of 20 to 90% by weight of water and
10 to 80% by weight of glycerol as a binder. 90. The process
according to embodiment 88 or 89, wherein the longest dimension of
the support body is 1 to 10 mm. 91. The process according to
embodiment 88 or
89, wherein the support body is a ring whose length is 4 to 10 mm,
whose external diameter is 2 to 10 mm and whose wall thickness is 1
to 4 mm. 92. The process according to embodiment 88 or 89, wherein
the support body is a ring whose length is 3 to 6 mm, whose
external diameter is 4 to 8 mm and whose wall thickness is 1 to 2
mm. 93. The process according to any of embodiments 87 to 92,
wherein the active multimetal oxide composition in the eggshell
catalyst forms an active composition shell of thickness 10 to 1000
.mu.m. 94. The process according to any of embodiments 87 to 93,
wherein the active multimetal oxide composition in the eggshell
catalyst forms an active composition shell of thickness 50 to 700
.mu.m. 95. The process according to any of embodiments 87 to 94,
wherein the active multimetal oxide composition in the eggshell
catalyst forms an active composition shell of thickness 100 to 600
.mu.m. 96. The process according to any of embodiments 87 to 95,
wherein the active multimetal oxide composition in the eggshell
catalyst forms an active composition shell of thickness 100 to 500
.mu.m. 97. The process according to any of embodiments 87 to 96,
wherein the active multimetal oxide composition in the eggshell
catalyst forms an active composition shell of thickness 150 to 300
.mu.m. 98. The process according to any of embodiments 1 to 97,
wherein the specific surface area of the active multimetal oxide
composition is .gtoreq.15 m.sup.2/g. 99. The process according to
any of embodiments 1 to 97, wherein the specific surface area of
the active multimetal oxide composition is .gtoreq.20 m.sup.2/g.
100. The process according to any of embodiments 1 to 97, wherein
the specific surface area of the active multimetal oxide
composition is .gtoreq.25 m.sup.2/g. 101. The process according to
any of embodiments 1 to 97, wherein the specific surface area of
the active multimetal oxide composition is .ltoreq.30 m.sup.2/g.
102. The process according to any of embodiments 1 to 101, wherein
the specific surface area of the active multimetal oxide
composition is .ltoreq.150 m.sup.2/g. 103. The process according to
any of embodiments 1 to 102, wherein the specific surface area of
the active multimetal oxide composition is .ltoreq.60 m.sup.2/g.
104. The process according to any of embodiments 1 to 103, wherein
the specific surface area of the active multimetal oxide
composition is .ltoreq.40 m.sup.2/g. 105. The process according to
any of embodiments 1 to 104, wherein the reaction temperature in
the heterogeneously catalyzed gas phase partial oxidation is in the
range of 200 to 400.degree. C. 106. The process according to any of
embodiments 1 to 105, wherein the reaction temperature in the
heterogeneously catalyzed gas phase partial oxidation is in the
range of 220 to 380.degree. C. 107. The process according to any of
embodiments 1 to 106, wherein the reaction temperature in the
heterogeneously catalyzed gas phase partial oxidation is in the
range of 230 to 350.degree. C. 108. The process according to any of
embodiments 1 to 107, wherein the reaction temperature in the
heterogeneously catalyzed gas phase partial oxidation is in the
range of 245 to 285.degree. C. 109. The process according to any of
embodiments 1 to 108, wherein the (meth)acrolein on commencement of
the gas phase partial oxidation is part of a reaction gas mixture
comprising molecular oxygen, with the proviso that the molar ratio
of molecular oxygen present in the reaction gas mixture to
(meth)acrolein present in the reaction gas mixture is 1 to 3. 110.
The process according to any of embodiments 1 to 109, wherein the
(meth)acrolein on commencement of the gas phase partial oxidation
is part of a reaction gas mixture also comprising steam. 111. The
process according to any of embodiments 1 to 110, wherein the
(meth)acrolein on commencement of the gas phase partial oxidation
is part of a reaction gas mixture comprising molecular oxygen,
inert gas and optionally steam, with the proviso that the
(meth)acrolein:oxygen:steam:inert gas volume ratio (l(STP)) present
in the reaction gas mixture is 1:(1 to 3):(0 to 20):(3 to 30). 112.
The process according to any of embodiments 1 to 111, wherein the
(meth)acrolein on commencement of the gas phase partial oxidation
is part of a reaction gas mixture comprising molecular oxygen,
inert gas and steam, with the proviso that the
(meth)acrolein:oxygen:steam:inert gas volume ratio (l(STP)) present
in the reaction gas mixture is 1:(1 to 3):(0.5 to 10):(7 to 10).
113. The process according to any of embodiments 1 to 112, wherein
the active multimetal oxide composition has a semicrystalline
structure. 114. The process according to any of embodiments 1 to
113, wherein a gas phase present in the pressure vessel during the
hydrothermal treatment has a steam content of at least 30% by
volume. 115. The process according to any of embodiments 1 to 113,
wherein a gas phase present in the pressure vessel during the
hydrothermal treatment has a steam content of at least 50% by
volume. 116. The process according to any of embodiments 1 to 113,
wherein a gas phase present in the pressure vessel during the
hydrothermal treatment has a steam content of at least 90% by
volume. 117. The process according to any of embodiments 1 to 113,
wherein a gas phase present in the pressure vessel during the
hydrothermal treatment has a steam content of at least 95% by
volume. 118. A multimetal oxide composition of the general formula
I
Mo.sub.12V.sub.aX.sup.1.sub.bX.sup.2.sub.cX.sup.3.sub.dX.sup.4.sub.eX.sup-
.5.sub.fX.sup.6.sub.gO.sub.n (I) in which the variables are each
defined as follows: X.sup.1=W, Nb, Ta, Cr and/or Ce, X.sup.2=Cu,
Ni, Co, Fe, Mn and/or Zn, X.sup.3=Sb, Te and/or Bi, X.sup.4=one or
more alkali metals (Li, Na, K, Rb and/or Cs) and/or H, X.sup.5=one
or more alkaline earth metals (Mg, Ca, Sr and/or Ba), X.sup.6=Si,
Al, Ti and/or Zr, a=1 to 6, b=0.2 to 8, c=0 to 18, d=0 to 40, e=0
to 4, f=0 to 4, g=0 to 40, and n=a number which is determined by
the valency and frequency of the elements in I other than oxygen,
where at least 50 mol % of the total molar amount of elements
X.sup.1 present in the multimetal oxide composition (I) is
accounted for by the element W, and the multimetal oxide
composition (I) is obtainable by a process in which a mixture of
sources of the elemental constituents of the multimetal oxide
composition (I) is subjected to a hydrothermal treatment in the
presence of water in a pressure vessel (as an aqueous mixture), the
newly forming solid is removed as a precursor composition and the
precursor composition is converted to the multimetal oxide
composition (I) by thermal treatment. 119. The multimetal oxide
composition according to embodiment 118, wherein at least 60 mol %
of the total molar amount of elements X.sup.1 present in the
multimetal oxide composition (I) is accounted for by the element W.
120. The multimetal oxide composition according to embodiment 118,
wherein at least 70 mol % of the total molar amount of elements
X.sup.1 present in the multimetal oxide composition (I) is
accounted for by the element W. 121. The multimetal oxide
composition according to embodiment 118, wherein at least 80 mol %
of the total molar amount of elements X.sup.1 present in the
multimetal oxide composition (I) is accounted for by the element W.
122. The multimetal oxide composition according to embodiment 118,
wherein at least 90 mol % of the total molar amount of elements
X.sup.1 present in the multimetal oxide composition (I) is
accounted for by the element W. 123. The multimetal oxide
composition according to embodiment 118, wherein at least 95 mol %
of the total molar amount of elements X.sup.1 present in the
multimetal oxide composition (I) is accounted for by the element W.
124. The multimetal oxide composition according to embodiment 118,
wherein 100 mol % of the total molar amount of elements X.sup.1
present in the multimetal oxide composition (I) is accounted for by
the element W. 125. The multimetal oxide composition according to
any of embodiments 118 to 124, wherein the stoichiometric
coefficient b is 0.2 to 4. 126. The multimetal oxide composition
according to any of embodiments 118 to 124, wherein the
stoichiometric coefficient b is 0.2 to 3. 127. The multimetal oxide
composition according to any of embodiments 118 to 126, wherein the
stoichiometric coefficient c is 0.5 to 18. 128. The multimetal
oxide composition according to any of embodiments 118 to 127,
wherein the stoichiometric coefficient c is 0.5 to 10. 129. The
multimetal oxide composition according to any of embodiments 118 to
128, wherein the stoichiometric coefficient c is 0.5 to 3. 130. The
multimetal oxide composition according to any of embodiments 118 to
129, wherein the stoichiometric coefficient a is 1 to 5. 131. The
multimetal oxide composition according to any of embodiments 118 to
130, wherein the stoichiometric coefficient a is 2 to 4. 132. The
multimetal oxide composition according to any of embodiments 118 to
131, wherein the stoichiometric coefficient d is 0 to 20. 133. The
multimetal oxide composition according to any of embodiments 118 to
132, wherein the stoichiometric coefficient d is 0 to 10. 134. The
multimetal oxide composition according to any of embodiments 118 to
133, wherein the stoichiometric coefficient d is 0 to 2. 135. The
multimetal oxide composition according to any of embodiments 118 to
134, wherein the stoichiometric coefficient e is 0 to 2. 136. The
multimetal oxide composition according to any of embodiments 118 to
135, wherein the stoichiometric coefficient f is 0 to 2. 137. The
multimetal oxide composition according to any of embodiments 118 to
136, wherein X.sup.1=W, Nb and/or Cr. 138. The multimetal oxide
composition according to any of embodiments 118 to 136, wherein
X.sup.1=W and Nb. 139. The multimetal oxide composition according
to any of embodiments 118 to 136, wherein X.sup.1=W. 140. The
multimetal oxide composition according to any of embodiments 118 to
139, wherein X.sup.2=Cu, Ni, Co and/or Fe. 141. The multimetal
oxide composition according to any of embodiments 118 to 139,
wherein X.sup.2=Cu and/or Ni. 142. The multimetal oxide composition
according to any of embodiments 118 to 139, wherein X.sup.2=Cu.
143. The multimetal oxide composition according to any of
embodiments 118 to 142, wherein X.sup.3=Sb. 144. The multimetal
oxide composition according to any of embodiments 118 to 143,
wherein X.sup.4=Na, K and/or H. 145. The multimetal oxide
composition according to any of embodiments 118 to 144, wherein
X.sup.5=Ca, Sr and/or Ba. 146. The multimetal oxide composition
according to any of embodiments 118 to 145, wherein X.sup.6=Si, Al
and/or Ti. 147. The multimetal oxide composition according to any
of embodiments 118 to 145, wherein X.sup.6=Si and/or Al. 148. The
multimetal oxide composition according to any of embodiments 118 to
124, wherein the variables of the general formula I are each
defined as follows: X.sup.1=W, Nb and/or Cr, X.sup.2=Cu, Ni, Co
and/or Fe X.sup.3=Sb, X.sup.4=Na, K and/or H, X.sup.5=Ca, Sr and/or
Ba, X.sup.6=Si, Al and/or Ti, a=1 to 5, b=0.2 to 4, c=0.5 to 18,
d=0 to 10, e=0 to 2, f=0 to 2, g=0 to 15, and n=a number which is
determined by the valency and frequency of the elements in the
general formula I other than oxygen. 149. The multimetal oxide
composition according to embodiment 148, wherein at least 50 mol %
of the total molar amount of elements X.sup.2 present in the
multimetal oxide composition (I) is accounted for by the element
Cu. 150. The multimetal oxide composition according to embodiment
148, wherein at least 70 mol % of the total molar amount of
elements X.sup.2 present in the multimetal oxide composition (I) is
accounted for by the element Cu. 151. The multimetal oxide
composition according to embodiment 148, wherein at least 90 mol %
of the total molar amount of elements X.sup.2 present in the
multimetal oxide composition (I) is accounted for by the element
Cu. 152. The multimetal oxide composition according to embodiment
148, wherein 100 mol % of the total molar amount of elements
X.sup.2 present in the multimetal oxide composition (I) is
accounted for by the element Cu. 153. The multimetal oxide
composition according to any of embodiments 118 to 124, wherein the
catalytically active multimetal oxide composition satisfies the
general stoichiometry II
Mo.sub.12V.sub.aX.sup.1.sub.bX.sup.2.sub.cX.sup.4.sub.eX.sup.5.sub.fX.sup-
.6.sub.gO.sub.n (II) in which the variables are each defined as
follows: X.sup.1=W and/or Nb, X.sup.2=Cu and/or Ni, X.sup.4=H,
X.sup.5=Ca and/or Sr, X.sup.6=Si and/or Al, a=2 to 4, b=0.2 to 3,
c=0.5 to 3, e=0 to 2, f=0 to 0.5, g=0 to 8, and n=a number which is
determined by the valency and frequency of the elements in the
general formula II other than oxygen. 154. The multimetal oxide
composition according to embodiment 153, wherein at least 50 mol %
of the total molar amount of elements X.sup.2 present in the
multimetal oxide composition is accounted for by the element Cu.
155. The multimetal oxide composition according to embodiment 153,
wherein at least 70 mol % of the total molar amount of elements
X.sup.2 present in the multimetal oxide composition is accounted
for by the element Cu. 156. The multimetal oxide composition
according to embodiment 153, wherein at least 90 mol % of the total
molar amount of elements X.sup.2 present in the multimetal oxide
composition is accounted for by the element Cu. 157. The multimetal
oxide composition according to embodiment 153, wherein 100 mol % of
the total molar amount of elements X.sup.2 present in the
multimetal oxide composition is accounted for by the element Cu.
158. The multimetal oxide composition according to any of
embodiments 118 to 124, wherein the catalytically active multimetal
oxide composition satisfies the general stoichiometry III
Mo.sub.12V.sub.aW.sub.bCu.sub.cX.sup.4.sub.eX.sup.5.sub.fX.sup.6.sub.gO.s-
ub.n (III) in which the variables are each defined as follows:
X.sup.4=one or more alkali metals (Li, Na, K, Rb and/or Cs) and/or
H, X.sup.5=one or more alkaline earth metals (Mg, Ca, Sr and/or
Ba), X.sup.6=one or more elements from the group of Si, Al, Ti and
Zr, a=2 to 4, b=0.2 to 3, c=0.5 to 2, e=0 to 4, f=0 to 4, with the
proviso that the sum of e and f does not exceed 4, g=0 to 40, and
n=a number which is determined by the valency and frequency of the
elements in the general formula Ill other than oxygen. 159. The
multimetal oxide composition according to embodiment 158, wherein
the stoichiometric coefficient b is 0.5 to 2. 160. The multimetal
oxide composition according to embodiment 158 or 159, wherein the
stoichiometric coefficient a is 2.5 to 3.5. 161. The multimetal
oxide composition according to any of embodiments 158 to 160,
wherein the stoichiometric coefficient c is 1 to 1.5. 162. The
multimetal oxide composition according to any of embodiments 118 to
161, wherein the hydrothermal treatment is effected at temperatures
in the range of >100.degree. C. to 600.degree. C. 163. The
multimetal oxide composition according to any of embodiments 118 to
162, wherein the hydrothermal treatment is effected at temperatures
in the range of .gtoreq.110.degree. C. to 400.degree. C. 164. The
multimetal oxide composition according to any of embodiments 118 to
163, wherein the hydrothermal treatment is effected at temperatures
in the range of .gtoreq.130.degree. C. to 300.degree. C. 165. The
multimetal oxide composition according to any of embodiments 118 to
164, wherein the hydrothermal treatment is effected at a
superatmospheric working pressure of .ltoreq.50 MPa. 166. The
multimetal oxide composition according to any of embodiments 118 to
165, wherein the hydrothermal treatment is effected at a working
pressure of .gtoreq.200 kPa and .ltoreq.25 MPa or at a working
pressure of .gtoreq.500 kPa and .ltoreq.22 MPa. 167. The multimetal
oxide composition according to any of embodiments 118 to 166,
wherein steam and liquid water coexist during the hydrothermal
treatment. 168. The multimetal oxide composition according to any
of embodiments 118 to 167, wherein the hydrothermally treated
aqueous mixture is a suspension. 169. The multimetal oxide
composition according to any of embodiments 118 to 167, wherein the
hydrothermally treated aqueous mixture is a solution. 170. The
multimetal oxide composition according to any of embodiments 118 to
169, wherein, based on the amount of water and sources of the
elemental constituents present in the pressure vessel during the
hydrothermal treatment, the proportion by weight of the total
amount of sources is at least 1% by weight. 171. The multimetal
oxide composition according to any of embodiments 118 to 170,
wherein, based on the amount of water and sources of the elemental
constituents present in the pressure vessel during the hydrothermal
treatment, the proportion by weight of the total amount of sources
is not more than 90% by weight. 172. The multimetal oxide
composition according to any of embodiments 118 to 171, wherein,
based on the amount of water and sources of the elemental
constituents present in the pressure vessel during the hydrothermal
treatment, the proportion by weight of the total amount of the
sources is 3 to 60% by weight. 173. The multimetal oxide
composition according to any of embodiments 118 to 172, wherein,
based on the amount of water and sources of the elemental
constituents present in the pressure vessel during the hydrothermal
treatment, the proportion by
weight of the total amount of the sources is 5 to 30% by weight.
174. The multimetal oxide composition according to any of
embodiments 118 to 173, wherein, based on the amount of water and
sources of the elemental constituents present in the pressure
vessel during the hydrothermal treatment, the proportion by weight
of the total amount of the sources is 5 to 15% by weight. 175. The
multimetal oxide composition according to any of embodiments 118 to
174, wherein the aqueous mixture subjected to the hydrothermal
treatment at 25.degree. C. and 103.1 kPa has a pH of <7. 176.
The multimetal oxide composition according to any of embodiments
118 to 174, wherein the aqueous mixture subjected to the
hydrothermal treatment at 25.degree. C. and 103.1 kPa has a pH of
.ltoreq.6. 177. The multimetal oxide composition according to any
of embodiments 118 to 174, wherein the aqueous mixture subjected to
the hydrothermal treatment at 25.degree. C. and 103.1 kPa has a pH
of .ltoreq.5. 178. The multimetal oxide composition according to
any of embodiments 118 to 174, wherein the aqueous mixture
subjected to the hydrothermal treatment at 25.degree. C. and 103.1
kPa has a pH of .ltoreq.4. 179. The multimetal oxide composition
according to any of embodiments 118 to 174, wherein the aqueous
mixture subjected to the hydrothermal treatment at 25.degree. C.
and 103.1 kPa has a pH of .ltoreq.3. 180. The multimetal oxide
composition according to any of embodiments 118 to 179, wherein the
aqueous mixture subjected to the hydrothermal treatment at
25.degree. C. and 103.1 kPa has a pH of .gtoreq.0. 181. The
multimetal oxide composition according to any of embodiments 118 to
180, wherein the aqueous mixture subjected to the hydrothermal
treatment at 25.degree. C. and 103.1 kPa has a pH of .gtoreq.1 and
.ltoreq.3. 182. The multimetal oxide composition according to any
of embodiments 118 to 181, wherein the aqueous mixture subjected to
the hydrothermal treatment at 25.degree. C. and 103.1 kPa has a pH
of .gtoreq.1.5 and .ltoreq.2.5. 183. The multimetal oxide
composition according to any of embodiments 175 to 182, wherein the
aqueous mixture subjected to the hydrothermal treatment comprises
added sulfuric acid. 184. The multimetal oxide composition
according to any of embodiments 118 to 183, wherein the aqueous
mixture subjected to the hydrothermal treatment is stirred during
the hydrothermal treatment. 185. The multimetal oxide composition
according to any of embodiments 118 to 184, wherein at least one
source of the elemental constituent Mo is ammonium heptamolybdate
and/or a hydrate of this compound. 186. The multimetal oxide
composition according to any of embodiments 118 to 185, wherein at
least one source of the elemental constituent W is ammonium
paratungstate, ammonium metatungstate and/or a hydrate of these
compounds. 187. The multimetal oxide composition according to any
of embodiments 118 to 186, wherein at least one source of the
elemental constituent vanadium comprises the vanadium in the +4
oxidation state. 188. The multimetal oxide composition according to
embodiment 187, wherein at least one source of the elemental
constituent vanadium is vanadyl sulfate and/or a hydrate of this
compound. 189. The multimetal oxide composition according to any of
embodiments 118 to 188, wherein at least one source of the
elemental constituent Cu is copper(II) sulfate, copper(II) nitrate,
copper(II) acetate and/or a hydrate of these compounds. 190. The
multimetal oxide composition according to any of embodiments 118 to
189, wherein the hydrothermal treatment takes 0.5 h to 100 h. 191.
The multimetal oxide composition according to any of embodiments
118 to 190, wherein the hydrothermal treatment takes 5 h to 80 h.
192. The multimetal oxide composition according to any of
embodiments 118 to 191, wherein the hydrothermal treatment is
effected in the absence or presence of molecular oxygen. 193. The
multimetal oxide composition according to any of embodiments 118 to
192, wherein the removal of the solid newly forming in the course
of hydrothermal treatment as the precursor composition comprises at
least one mechanical removal of this solid and at least one washing
operation on the mechanically removed solid with at least one wash
liquid from the group consisting of organic acids, inorganic acids
and aqueous solutions of the acids mentioned. 194. The multimetal
oxide composition according to embodiment 193, wherein the wash
liquid is an aqueous solution of oxalic acid. 195. The multimetal
oxide composition according to any of embodiments 118 to 194,
wherein the temperature in the course of thermal treatment of the
precursor composition is 300 to 700.degree. C. 196. The multimetal
oxide composition according to any of embodiments 118 to 195,
wherein the temperature in the course of thermal treatment of the
precursor composition is 350 to 650.degree. C. 197. The multimetal
oxide composition according to any of embodiments 118 to 196,
wherein the temperature in the course of thermal treatment of the
precursor composition is 400 to 600.degree. C. 198. The multimetal
oxide composition according to any of embodiments 118 to 197,
wherein the thermal treatment of the precursor composition is
effected under a gas atmosphere comprising molecular oxygen. 199.
The multimetal oxide composition according to any of embodiments
118 to 197, wherein the thermal treatment of the precursor
composition is effected under reduced pressure or under a gas
atmosphere which does not comprise any molecular oxygen. 200. The
multimetal oxide composition according to any of embodiments 118 to
197, wherein the thermal treatment of the precursor composition is
effected under a reducing gas atmosphere. 201. The multimetal oxide
composition according to any of embodiments 198 to 200, wherein the
thermal treatment of the precursor composition is effected under a
gas atmosphere comprising molecular nitrogen and/or noble gas. 202.
The multimetal oxide composition according to any of embodiments
118 to 197, wherein the thermal treatment of the precursor
composition is effected under a gas atmosphere whose content of
molecular oxygen and reducing constituents is in each case
.ltoreq.3% by volume. 203. The multimetal oxide composition
according to any of embodiments 118 to 202, wherein the specific
surface area of the multimetal oxide composition is .gtoreq.15
m.sup.2/g. 204. The multimetal oxide composition according to any
of embodiments 118 to 202, wherein the specific surface area of the
multimetal oxide composition is .gtoreq.20 m.sup.2/g. 205. The
multimetal oxide composition according to any of embodiments 118 to
202, wherein the specific surface area of the multimetal oxide
composition is .gtoreq.25 m.sup.2/g. 206. The multimetal oxide
composition according to any of embodiments 118 to 202, wherein the
specific surface area of the multimetal oxide composition is
.gtoreq.30 m.sup.2/g. 207. The multimetal oxide composition
according to any of embodiments 118 to 206, wherein the specific
surface area of the multimetal oxide composition is .ltoreq.150
m.sup.2/g. 208. The multimetal oxide composition according to any
of embodiments 118 to 207, wherein the specific surface area of the
multimetal oxide composition is .ltoreq.60 m.sup.2/g. 209. The
multimetal oxide composition according to any of embodiments 118 to
208, wherein the specific surface area of the multimetal oxide
composition is .ltoreq.40 m.sup.2/g. 210. The multimetal oxide
composition according to any of embodiments 118 to 209, which has a
semicrystalline structure. 211. The multimetal oxide composition
according to any of embodiments 118 to 210, wherein a gas phase
present in the pressure vessel during the hydrothermal treatment
has a steam content of at least 30% by volume. 212. The multimetal
oxide composition according to any of embodiments 118 to 210,
wherein a gas phase present in the pressure vessel during the
hydrothermal treatment has a steam content of at least 50% by
volume. 213. The multimetal oxide composition according to any of
embodiments 118 to 210, wherein a gas phase present in the pressure
vessel during the hydrothermal treatment has a steam content of at
least 90% by volume. 214. The multimetal oxide composition
according to any of embodiments 118 to 210, wherein a gas phase
present in the pressure vessel during the hydrothermal treatment
has a steam content of at least 95% by volume. 215. The use of a
multimetal oxide composition according to any of embodiments 118 to
214 as a catalytic active composition for the performance of a
heterogeneously catalyzed gas phase partial oxidation of
(meth)acrolein to (meth)acrylic acid. 216. An eggshell catalyst
consisting of a support body and a catalytic active composition
applied to the surface of the support body, and optionally binders
for application of the active composition to the surface of the
support body, wherein the catalytic active composition is a
multimetal oxide composition according to any of embodiments 118 to
214. 217. The eggshell catalyst according to embodiment 216,
wherein the multimetal oxide composition in the eggshell catalyst
has been applied to a spherical or annular support body. 218. The
eggshell catalyst according to embodiment 216 or 217, wherein the
multimetal oxide composition has been applied to the support body
with a solution composed of 20 to 90% by weight of water and 10 to
80% by weight of glycerol as a binder. 219. The eggshell catalyst
according to any of embodiments 216 to 218, wherein the longest
dimension of the support body is 1 to 10 mm. 220. The eggshell
catalyst according to any of embodiments 216 to 219, wherein the
support body is a ring whose length is 4 to 10 mm, whose external
diameter is 2 to 10 mm and whose wall thickness is 1 to 4 mm. 221.
The eggshell catalyst according to embodiment 216 or 219, wherein
the support body is a ring whose length is 3 to 6 mm, whose
external diameter is 4 to 8 mm and whose wall thickness is 1 to 2
mm. 222. The eggshell catalyst according to any of embodiments 216
to 221, wherein the multimetal oxide composition in the eggshell
catalyst forms an active composition shell of thickness 10 to 1000
.mu.m. 223. The eggshell catalyst according to any of embodiments
216 to 222, wherein the multimetal oxide composition in the
eggshell catalyst forms an active composition shell of thickness 50
to 700 .mu.m. 224. The eggshell catalyst according to any of
embodiments 216 to 223, wherein the multimetal oxide composition in
the eggshell catalyst forms an active composition shell of
thickness 100 to 600 .mu.m. 225. The eggshell catalyst according to
any of embodiments 216 to 224, wherein the multimetal oxide
composition in the eggshell catalyst forms an active composition
shell of thickness 100 to 500 .mu.m. 226. The eggshell catalyst
according to any of embodiments 216 to 225, wherein the active
multimetal oxide composition in the eggshell catalyst forms an
active composition shell of thickness 150 to 300 .mu.m. 227. The
use of an eggshell catalyst according to any of embodiments 216 to
226 as a catalyst for the performance of a heterogeneously
catalyzed gas phase partial oxidation of (meth)acrolein to
(meth)acrylic acid. 228. A process for preparing a multimetal oxide
composition of the general formula I
Mo.sub.12V.sub.aX.sup.1.sub.bX.sup.2.sub.cX.sup.3.sub.dX.sup.4.sub.eX.sup-
.5.sub.fX.sup.6.sub.gO.sub.n (I) in which the variables are each
defined as follows: X.sup.1=W, Nb, Ta, Cr and/or Ce, X.sup.2=Cu,
Ni, Co, Fe, Mn and/or Zn, X.sup.3=Sb, Te and/or Bi, X.sup.4=one or
more alkali metals (Li, Na, K, Rb and/or Cs) and/or H, X.sup.5=one
or more alkaline earth metals (Mg, Ca, Sr and/or Ba), X.sup.6=Si,
Al, Ti and/or Zr, a=1 to 6, b=0.2 to 8, c=0 to 18, d=0 to 40, e=0
to 4, f=0 to 4, g=0 to 40, and n=a number which is determined by
the valency and frequency of the elements in I other than oxygen,
wherein at least 50 mol % of the total molar amount of elements
X.sup.1 present in the multimetal oxide composition (I) is
accounted for by the element W, and the multimetal oxide
composition (I) is obtained by subjecting a mixture of sources of
the elemental constituents of the multimetal oxide composition (I)
to a hydrothermal treatment in the presence of water in a pressure
vessel (as an aqueous mixture), removing the newly forming solid as
a precursor composition and converting the precursor composition to
the multimetal oxide composition (I) by thermal treatment. 228. The
process according to embodiment 227, wherein at least 60 mol % of
the total molar amount of elements X.sup.1 present in the
multimetal oxide composition (I) is accounted for by the element W.
229. The process according to embodiment 227, wherein at least 70
mol % of the total molar amount of elements X.sup.1 present in the
multimetal oxide composition (I) is accounted for by the element W.
230. The process according to embodiment 227, wherein at least 80
mol % of the total molar amount of elements X.sup.1 present in the
multimetal oxide composition (I) is accounted for by the element W.
231. The process according to embodiment 227, wherein at least 90
mol % of the total molar amount of elements X.sup.1 present in the
multimetal oxide composition (I) is accounted for by the element W.
232. The process according to embodiment 227, wherein at least 95
mol % of the total molar amount of elements X.sup.1 present in the
multimetal oxide composition (I) is accounted for by the element W.
233. The process according to embodiment 227, wherein 100 mol % of
the total molar amount of elements X.sup.1 present in the
multimetal oxide composition (I) is accounted for by the element W.
234. The process according to any of embodiments 227 to 233,
wherein the stoichiometric coefficient b is 0.2 to 4. 235. The
process according to any of embodiments 227 to 233, wherein the
stoichiometric coefficient b is 0.2 to 3. 236. The process
according to any of embodiments 227 to 235, wherein the
stoichiometric coefficient c is 0.5 to 18. 237. The process
according to any of embodiments 227 to 235, wherein the
stoichiometric coefficient c is 0.5 to 10. 238. The process
according to any of embodiments 227 to 235, wherein the
stoichiometric coefficient c is 0.5 to 3. 239. The process
according to any of embodiments 227 to 238, wherein the
stoichiometric coefficient a is 1 to 5. 240. The process according
to any of embodiments 227 to 239, wherein the stoichiometric
coefficient a is 2 to 4. 241. The process according to any of
embodiments 227 to 240, wherein the stoichiometric coefficient d is
0 to 20. 242. The process according to any of embodiments 227 to
240, wherein the stoichiometric coefficient d is 0 to 10. 243. The
process according to any of embodiments 227 to 240, wherein the
stoichiometric coefficient d is 0 to 2. 244. The process according
to any of embodiments 227 to 240, wherein the stoichiometric
coefficient e is 0 to 2. 245. The process according to any of
embodiments 227 to 244, wherein the stoichiometric coefficient f is
0 to 2. 246. The process according to any of embodiments 227 to
245, wherein X.sup.1=W, Nb and/or Cr. 247. The process according to
any of embodiments 227 to 245, wherein X.sup.1=W and Nb. 248. The
process according to any of embodiments 227 to 245, wherein
X.sup.1=W. 249. The process according to any of embodiments 227 to
248, wherein X.sup.2=Cu, Ni, Co and/or Fe. 250. The process
according to any of embodiments 227 to 248, wherein X.sup.2=Cu
and/or Ni. 251. The process according to any of embodiments 227 to
248, wherein X.sup.2=Cu. 252. The process according to any of
embodiments 227 to 251, wherein X.sup.3=Sb. 253. The process
according to any of embodiments 227 to 252, wherein X.sup.4=Na, K
and/or H. 254. The process according to any of embodiments 227 to
253, wherein X.sup.5=Ca, Sr and/or Ba. 255. The process according
to any of embodiments 227 to 254, wherein X.sup.6=Si, Al and/or Ti.
256. The process according to any of embodiments 227 to 254,
wherein X.sup.6=Si and/or Al. 257. The process according to any of
embodiments 227 to 233, wherein the variables of the general
formula I are each defined as follows: X.sup.1=W, Nb and/or Cr,
X.sup.2=Cu, Ni, Co and/or Fe X.sup.3=Sb, X.sup.4=Na, K and/or H,
X.sup.5=Ca, Sr and/or Ba, X.sup.6=Si, Al and/or Ti, a=1 to 5, b=0.2
to 4, c=0.5 to 18, d=0 to 10, e=0 to 2, f=0 to 2, g=0 to 15, and
n=a number which is determined by the valency and frequency of the
elements in the general formula I other than oxygen. 258. The
process according to embodiment 257, wherein at least 50 mol % of
the total molar amount of elements X.sup.2 present in the
multimetal oxide composition (I) is accounted for by the element
Cu. 259. The process according to embodiment 257, wherein at least
70 mol % of the total molar amount of elements X.sup.2 present in
the multimetal oxide composition (I) is accounted for by the
element Cu. 260. The process according to embodiment 257, wherein
at least 90 mol % of the total molar amount of elements X.sup.2
present in the multimetal oxide composition (I) is accounted for by
the element Cu. 261. The process according to embodiment 257,
wherein 100 mol % of the total molar amount of elements X.sup.2
present in the multimetal oxide composition (I) is accounted for by
the element Cu. 262. The process according to any of embodiments
227 to 233, wherein the catalytically active multimetal oxide
composition satisfies the general stoichiometry II
Mo.sub.12V.sub.aX.sup.1.sub.bX.sup.2.sub.cX.sup.4.sub.eX.sup.5.sub.fX.sup-
.6.sub.gO.sub.n (II) in which the variables are each defined as
follows: X.sup.1=W and/or Nb, X.sup.2=Cu and/or Ni, X.sup.4=H,
X.sup.5=Ca and/or Sr, X.sup.6=Si and/or Al, a=2 to 4, b=0.2 to 3,
c=0.5 to 3, e=0 to 2, f=0 to 0.5, g=0 to 8, and n=a number which is
determined by the valency and frequency of the elements in the
general formula II other than oxygen. 263. The process according to
embodiment 262, wherein at least 50 mol % of the total molar amount
of elements X.sup.2 present in the multimetal oxide composition is
accounted for by the element Cu. 264. The process according to
embodiment 262, wherein at least 70 mol % of the total molar amount
of elements X.sup.2 present in the multimetal oxide composition is
accounted for by the element Cu. 265. The process according to
embodiment 262, wherein at least 90 mol % of the total molar amount
of elements X.sup.2 present in the multimetal oxide composition is
accounted for by the element Cu. 266. The process according to
embodiment 262, wherein 100 mol % of the total molar amount of
elements X.sup.2 present in the multimetal oxide composition is
accounted for by the element Cu. 267. The process according to any
of embodiments 227 to 233, wherein the catalytically active
multimetal oxide composition satisfies the general stoichiometry
III
Mo.sub.12V.sub.aW.sub.bCu.sub.cX.sup.4.sub.eX.sup.5.sub.fX.sup.6.sub.gO.s-
ub.n (III) in which the variables are each defined as follows:
X.sup.4=one or more alkali metals (Li, Na, K, Rb and/or Cs) and/or
H, X.sup.5=one or more alkaline earth metals (Mg, Ca, Sr and/or
Ba), X.sup.6=one or more elements from the group of Si, Al, Ti and
Zr, a=2 to 4, b=0.2 to 3, c=0.5 to 2, e=0 to 4, f=0 to 4, with the
proviso that the sum of e and f does not exceed 4, g=0 to 40, and
n=a number which is determined by the valency and frequency of the
elements in the general formula III other than oxygen. 268. The
process according to embodiment 267, wherein the stoichiometric
coefficient b is 0.5 to 2. 269. The process according to embodiment
267 or 268, wherein the stoichiometric coefficient a is 2.5 to 3.5.
270. The process according to any of embodiments 267 to 269,
wherein the stoichiometric coefficient c is 1 to 1.5. 271. The
process according to any of embodiments 227 to 270, wherein the
hydrothermal treatment is effected at temperatures in the range of
>100.degree. C. to 600.degree. C. 272. The process according to
any of embodiments 227 to 271, wherein the hydrothermal treatment
is effected at temperatures in the range of .gtoreq.110.degree. C.
to 400.degree. C. 273. The process according to any of embodiments
227 to 272, wherein the hydrothermal treatment is effected at
temperatures in the range of .gtoreq.130.degree. C. to 300.degree.
C. 274. The process according to any of embodiments 227 to 273,
wherein the hydrothermal treatment is effected at a
superatmospheric working pressure of .ltoreq.50 MPa. 275. The
process according to any of embodiments 227 to 274, wherein the
hydrothermal treatment is effected at a working pressure of
.gtoreq.200 kPa and .ltoreq.25 MPa or at a working pressure of
.gtoreq.500 kPa and .ltoreq.22 MPa. 276. The process according to
any of embodiments 227 to 275, wherein steam and liquid water
coexist during the hydrothermal treatment. 277. The process
according to any of embodiments 227 to 276, wherein the
hydrothermally treated aqueous mixture is a suspension. 278. The
process according to any of embodiments 227 to 276, wherein the
hydrothermally treated aqueous mixture is a solution. 279. The
process according to any of embodiments 227 to 278, wherein, based
on the amount of water and sources of the elemental constituents
present in the pressure vessel during the hydrothermal treatment,
the proportion by weight of the total amount of sources is at least
1% by weight. 280. The process according to any of embodiments 227
to 279, wherein, based on the amount of water and sources of the
elemental constituents present in the pressure vessel during the
hydrothermal treatment, the proportion by weight of the total
amount of sources is not more than 90% by weight. 281. The process
according to any of embodiments 227 to 280, wherein, based on the
amount of water and sources of the elemental constituents present
in the pressure vessel during the hydrothermal treatment, the
proportion by weight of the total amount of the sources is 3 to 60%
by weight. 282. The process according to any of embodiments 227 to
280, wherein, based on the amount of water and sources of the
elemental constituents present in the pressure vessel during the
hydrothermal treatment, the proportion by weight of the total
amount of the sources is 5 to 30% by weight. 283. The process
according to any of embodiments 227 to 282, wherein, based on the
amount of water and sources of the elemental constituents present
in the pressure vessel during the hydrothermal treatment, the
proportion by weight of the total amount of the sources is 5 to 15%
by weight. 284. The process according to any of embodiments 227 to
283, wherein the aqueous mixture subjected to the hydrothermal
treatment at 25.degree. C. and 103.1 kPa has a pH of <7. 285.
The process according to any of embodiments 227 to 283, wherein the
aqueous mixture subjected to the hydrothermal treatment at
25.degree. C. and 103.1 kPa has a pH of .ltoreq.6. 286. The process
according to any of embodiments 227 to 283, wherein the aqueous
mixture subjected to the hydrothermal treatment at 25.degree. C.
and 103.1 kPa has a pH of .ltoreq.5. 287. The process according to
any of embodiments 227 to 283, wherein the aqueous mixture
subjected to the hydrothermal treatment at 25.degree. C. and 103.1
kPa has a pH of .ltoreq.4. 288. The process according to any of
embodiments 227 to 283, wherein the aqueous mixture subjected to
the hydrothermal treatment at 25.degree. C. and 103.1 kPa has a pH
of .ltoreq.3. 289. The process according to any of embodiments 227
to 288, wherein the aqueous mixture subjected to the hydrothermal
treatment at 25.degree. C. and 103.1 kPa has a pH of .gtoreq.0.
290. The process according to any of embodiments 227 to 289,
wherein the aqueous mixture subjected to the hydrothermal treatment
at 25.degree. C. and 103.1 kPa has a pH of .gtoreq.1 and .ltoreq.3.
291. The process according to any of embodiments 227 to 290,
wherein the aqueous mixture subjected to the hydrothermal treatment
at 25.degree. C. and 103.1 kPa has a pH of .gtoreq.1.5 and
.ltoreq.2.5. 292. The process according to any of embodiments 227
to 291, wherein the aqueous mixture subjected to the hydrothermal
treatment comprises added sulfuric acid. 293. The process according
to any of embodiments 227 to 292, wherein the aqueous mixture
subjected to the hydrothermal treatment is stirred during the
hydrothermal treatment. 294. The process according to any of
embodiments 227 to 293, wherein at least one source of the
elemental constituent Mo is ammonium heptamolybdate and/or a
hydrate of this compound. 295. The process according to any of
embodiments 227 to 294, wherein at least one source of the
elemental constituent W is ammonium paratungstate, ammonium
metatungstate and/or a hydrate of these compounds. 296. The process
according to any of embodiments 227 to 295, wherein at least one
source of the elemental constituent vanadium comprises the vanadium
in the +4 oxidation state. 297. The process according to embodiment
296, wherein at least one source of the elemental constituent
vanadium is vanadyl sulfate and/or a hydrate of this compound. 298.
The process according to any of embodiments 227 to 297, wherein at
least one source of the elemental constituent Cu is copper(II)
sulfate, copper(II) nitrate, copper(II) acetate and/or a hydrate of
these compounds. 299. The process according to any of embodiments
227 to 298, wherein the hydrothermal treatment takes 0.5 h to 100
h. 300. The process according to any of embodiments 227 to 299,
wherein the hydrothermal treatment takes 5 h to 80 h. 301. The
process according to any of embodiments 227 to 300, wherein the
hydrothermal treatment is effected in the absence or presence of
molecular oxygen. 302. The process according to any of embodiments
227 to 301, wherein the removal of the solid newly formed in the
course of hydrothermal treatment as the precursor composition
comprises at least one mechanical removal of this solid and at
least one washing operation on the mechanically removed solid with
at least one wash liquid from the group consisting of organic
acids, inorganic acids and aqueous solutions of the acids
mentioned. 303. The process according to embodiment 302, wherein
the wash liquid is an aqueous solution of oxalic acid. 304. The
process according to any of embodiments 227 to 303, wherein the
temperature in the course of thermal treatment of the precursor
composition is 300 to 700.degree. C. 305. The process according to
any of embodiments 227 to 304, wherein the temperature in the
course of thermal treatment of the precursor composition is 350 to
650.degree. C. 306. The process according to any of embodiments 227
to 305, wherein the temperature in the course of thermal treatment
of the precursor composition is 400 to 600.degree. C. 307. The
process according to any of embodiments 227 to 306, wherein the
thermal treatment of the precursor composition is effected under a
gas atmosphere comprising molecular oxygen. 308. The process
according to any of embodiments 227 to 306, wherein the thermal
treatment of the precursor composition is effected under reduced
pressure or under a gas atmosphere which does not comprise any
molecular oxygen. 309. The process according to any of embodiments
227 to 306, wherein the thermal treatment of the precursor
composition is effected under a reducing gas atmosphere. 310. The
process according to any of embodiments 307 to 309, wherein the
thermal treatment of the precursor composition is effected under a
gas atmosphere comprising molecular nitrogen and/or noble gas. 311.
The process according to any of embodiments 227 to 306, wherein the
thermal treatment of the precursor composition is effected under a
gas atmosphere whose content of molecular oxygen and reducing
constituents is in each case .ltoreq.3% by volume. 312. The process
according to any of embodiments 227 to 311, wherein a gas phase
present in the pressure vessel during the hydrothermal treatment
has a steam content of at least 30% by volume. 313. The process
according to any of embodiments 227 to 311, wherein a gas phase
present in the pressure vessel during the hydrothermal treatment
has a steam content of at least 50% by volume. 314. The process
according to any of embodiments 227 to 311, wherein a gas phase
present in the pressure vessel during the hydrothermal treatment
has a steam content of at least 90% by volume. 315. The process
according to any of embodiments 227 to 311, wherein a gas phase
present in the pressure vessel during the hydrothermal treatment
has a steam content of at least 95% by volume. 316. A process for
producing an eggshell catalyst by applying a finely divided
multimetal oxide to the surface of a support body with the aid of a
liquid binder, wherein the finely divided multimetal oxide is a
multimetal oxide composition according to any of embodiments 118 to
214. 317. The process according to embodiment 316, wherein the
support body is spherical or annular. 318. The process according to
embodiment 316 or 317, wherein the liquid binder is a solution
composed of 20 to 90% by weight of water and 10 to 80% by weight of
glycerol. 319. The process according to any of embodiments 316 to
318, wherein the longest dimension of the support body is 1 to 10
mm. 320. The process according to any of embodiments 316 to 319,
wherein the support body is a ring whose length is 4 to 10 mm,
whose external diameter is 2 to 10 mm and whose wall thickness is 1
to 4 mm. 321. The process according to either of embodiments 316
and 319, wherein the support body is a ring whose length is 3 to 6
mm, whose external diameter is 4 to 8 mm and whose wall thickness
is 1 to 2 mm. 322. The process according to any of embodiments 316
to 321, wherein the multimetal oxide composition is applied to the
surface of the support body as an active composition shell of
thickness 10 to 1000 .mu.m. 323. The process according to any of
embodiments 316 to 322, wherein the multimetal oxide composition is
applied to the surface of the support body as an active composition
shell of thickness 50 to 700 .mu.m. 324. The process according to
any of embodiments 316 to 323, wherein the multimetal oxide
composition is applied to the surface of the support body as an
active composition shell of thickness 100 to 600 .mu.m. 325. The
process according to any of embodiments 316 to 324, wherein the
multimetal oxide composition is applied to the surface of the
support body as an active composition shell of thickness 100 to 500
.mu.m. 326. The process according to any of embodiments 316 to 325,
wherein the multimetal oxide composition is applied to the surface
of the support body as an active composition shell of thickness 150
to 300 .mu.m. 327. A process for heterogeneously catalyzed gas
phase partial oxidation of (meth)acrolein to (meth)acrylic acid
over a catalytically active multimetal oxide composition, wherein
the multimetal oxide composition is a multimetal oxide composition
according to any of embodiments 118 to 214. 328. A process for
heterogeneously catalyzed gas phase partial oxidation of
(meth)acrolein to (meth)acrylic acid over an eggshell catalyst,
wherein the eggshell catalyst is an eggshell catalyst according to
any of embodiments 316 to 326.
U.S. Provisional Patent Application No. 61/645082, filed May 10,
2012, is incorporated into the present patent application by
literature reference.
With regard to the above mentioned teachings, numerous changes and
deviations from the present invention are possible. It can
therefore be assumed that the invention, within the scope of the
appended claims, can be performed differently than the way
described specifically herein.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows the cross section of an inner tube.
FIG. 2 shows a plot of the yield Y.sup.AA of acrylic acid as a
function of the respective catalyst bed temperature both for the
first (reference numeral 1 in FIG. 2) and the third (reference
numeral 3 in FIG. 2) TP partial oxidation cycle.
FIG. 3 shows an X-ray diffractogram of a multimetal oxide prepared
according to one embodiment of the invention.
FIG. 4 shows an X-ray diffractogram of a multimetal oxide prepared
according to one embodiment of the invention with a different scale
from FIG. 3.
FIG. 5 shows an X-ray diffractogram of a comparative multimetal
oxide.
FIG. 6 shows an X-ray diffractogram of a multimetal oxide prepared
according to one embodiment of the invention.
FIG. 7 shows a plot of the yield Y.sup.AA of acrylic acid as a
function of the respective catalyst bed temperature in the third TP
partial oxidation cycle, for the long-term operation both from 2.d)
(reference numeral 1 in FIG. 7) and from 3.d) (reference numeral 2
in FIG. 7), and from 5. (reference numeral 3 in FIG. 7).
EXAMPLES AND COMPARATIVE EXAMPLES
1. Hydrothermal preparation of a comparative mixed oxide of the
stoichiometry Mo.sub.12V.sub.4O.sub.x and analysis of the
performance thereof in long-term operation of a partial oxidation
of acrolein to acrylic acid heterogeneously catalyzed thereby a)
Preparation of the aqueous mixture for hydrothermal treatment
First of all, 8.83 g (=50 mmol of Mo) of ammonium heptamolybdate
tetrahydrate [(NH.sub.4).sub.6Mo.sub.7O.sub.24.4H.sub.2O] were
dissolved in 120 ml of water at 25.degree. C. Once the resulting
yellow solution had been stirred thereafter at 25.degree. C. for a
further 30 minutes, it formed a first aqueous solution. Dissolution
of 3.28 g of a vanadyl sulfate hydrate (=12.5 mmol of V) in 120 ml
of water at 25.degree. C. produced a second aqueous solution. While
constantly stirring the first aqueous solution with maintenance of
the 25.degree. C., the second aqueous solution was continuously
added dropwise to the first aqueous solution within 15 minutes. The
color of the resulting mixed solution was dark violet.
The mixed solution was stirred at 25.degree. C. for a further 30
minutes. Subsequently, the pH of the mixed solution was adjusted to
the value of 2.2 by adding dilute aqueous sulfuric acid at
25.degree. C. (the concentration of which was about 1 molar). All
aforementioned working steps were performed under air.
Finally, the molecular oxygen present dissolved in the resulting
acidic mixed solution was displaced by bubbling through a nitrogen
stream at 25.degree. C. (.gtoreq.99.9 mol % of N.sub.2; approx.
1500 ml/h) for 10 minutes. The final solution thus obtained was
subsequently treated hydrothermally as described below. b)
Hydrothermal treatment of the aqueous final solution obtained in
1.a)
The shell of the reaction space in the autoclave was manufactured
from Teflon and had the geometry of a hollow circular cylinder with
a removable lid which was sealed with a Viton.RTM. O-ring. The wall
thickness of the casing of the hollow Teflon cylinder was 7.5 mm,
the internal diameter thereof was 60 mm, the base was 5.0 mm thick
and the volume of the reaction space was 325 ml. The hollow Teflon
cylinder was surrounded by a pressure-resistant casing with a lid
which can be screwed on in a pressure-tight manner. The material
from which it was manufactured was DIN 1.4301 stainless steel.
Through the two lids, a Teflon-sheathed thermocouple was conducted
into the reaction space (K type from TMH GmbH in D-63477 Maintal),
with which the temperature in the reaction space was registered.
The reaction interior was equipped with a Teflon-sheathed magnetic
bar which could be set in rotating motion with the aid of a
customary laboratory magnetic stirrer plate, in order to stir the
reaction space. The heating was effected by means of four
electrical heating cartridges (230 V, 400 W, from Heinz Stegmaier
GmbH in D-78567 Fridingen), in two half-shell-shaped sleeves of
aluminum (as the heating jacket), which surrounded the
pressure-resistant stainless steel casing. To control the
temperature program, a programmable process regulator (CAL 9500 P
type from CAL Control Inc., Libertyville, Ill., 60048-3764, U.S.A.)
was used. For temperature monitoring for this purpose, a further
thermocouple was mounted in a fixed manner in the heating jacket.
An additional thermocouple in the heating jacket served for
safeguarding from excess temperature.
The aqueous final solution produced in 1.a) was introduced in its
entirety, with a temperature of 25.degree. C., into the ventilated
reaction space of the autoclave. Subsequently, the autoclave
including the reaction space was sealed pressure-tight. Thereafter,
the solution stirred within the reaction space of the autoclave was
heated at a heating rate of 5.degree. C./min to a temperature of
175.degree. C. and then held at this temperature (175.degree. C.)
while stirring over a further 24 h. Then the heating was ended and
the contents of the reaction space were cooled in an essentially
linear manner to 25.degree. C. while continuing to stir within 7 h.
The maximum operating pressure was about 1 MPa.
In the reaction space was an aqueous suspension. By filtration, the
suspended solids were removed. The filtercake obtained was slurried
in 120 ml of an aqueous oxalic acid solution at a temperature of
80.degree. C. (oxalic acid concentration=0.4 mol/l solution (based
on 25.degree. C. and 101.3 kPa)) and the mixture was stirred while
maintaining the 80.degree. C. over a period of 1 h. Then the solids
were filtered off again and washed with 200 ml of water, the
temperature of which was 25.degree. C. Subsequently, the solids
were dried at a temperature of 80.degree. C. in a forced-air drying
cabinet for 10 h to give the precursor composition for the thermal
treatment. c) Thermal treatment (calcination) of the precursor
composition obtained in 1.b)
The apparatus for thermal treatment comprised a quartz glass inner
tube rotatable about its own longitudinal axis and an outer tube
surrounding this inner tube.
The length of the outer tube was 52 cm. At a length of 36 cm the
internal diameter of the outer tube was 4.8 cm, and at a length of
15 cm the internal diameter of the outer tube was 6.5 cm. The
transition from internal diameter 4.8 cm to internal diameter 6.5
cm occurred over a length of 1 cm. At that end of the outer tube
(the end E1) at which the outer tube had the greater cross section,
the outer tube was closed with a quartz glass base. At the end
opposite this end (the end E2), at which the outer tube had the
smaller cross section, the outer tube was open.
The inner tube had a length of 49 cm. At a length of 37 cm, the
internal diameter of the inner tube was 1.5 cm. For a subsequent
length of 10 cm, the internal diameter of the shell of the inner
tube was 3.4 cm (for this longitudinal section, the cross section
of the inner tube was not circular but as shown in FIG. 1 of this
document; this cross-sectional configuration was required by the
action of a static stirrer) and, for a subsequent end length of 2
cm, the internal diameter of the inner tube was 1 cm.
The inner tube was open at both sides (ends). The glass thickness
in both quartz glass tubes was 1.5 mm.
At the end E2 of the outer tube, the inner tube was conducted into
the outer tube with its orifice having the smaller cross section
leading, such that the longitudinal axes of both tubes coincided
and a distance from the orifice of the smaller cross section of the
inner tube to the glass base of the outer tube of 2 cm
remained.
The dry precursor composition from 1.b), prior to the thermal
treatment thereof, was triturated in a mortar and then introduced
in its entirety into the section of the aforementioned inner tube
which had a cross section according to FIG. 1, and fixed therein
with quartz wool on both sides.
A glass-metal connection was used to secure the two glass tubes at
the open side of the outer tube to a screw motor (from Faulhaber in
D-71101 Schonach), which was able to rotate about its own axis at
constant rotational speed. A Cr/Ni thermocouple which projected
into the finely divided precursor composition controlled the
temperature in the calcination material (in the precursor
composition) using a Eurothermregler.RTM..
At a length of 35 cm, with the bulging part thereof leading, the
outer tube (and with it the inner tube) projected into a heatable
muffle furnace from Heraeus.
From the side of the screw motor, it was possible to conduct a
nitrogen stream (>99.95% by volume of N.sub.2) into the inner
tube, which flowed out of it again at the opposite end of the inner
tube, with a flow rate controllable by means of a variable area
flowmeter. Any gases released from the precursor composition during
the calcining operation (the thermal treatment) and the nitrogen
stream flowing out of the inner tube were removable via the outer
tube.
At a nitrogen volume flow rate of 100 ml/min (this was supplied at
a temperature of 25.degree. C.) and a speed of the screw motor of 3
revolutions/min, the finely divided precursor composition (after it
had been purged with the nitrogen stream for 30 min beforehand) was
heated at a heating rate of 5.degree. C./min to 500.degree. C.
Subsequently, this temperature (the 500.degree. C.) was maintained
while retaining the nitrogen stream for a further 120 min. Finally,
the calcination material was cooled in an essentially linear manner
to 25.degree. C. within 10 h.
The particle sizes of the resulting comparative mixed oxide were in
the range from 3 to 25 .mu.m (longest dimension). The specific
surface area SA was 66 m.sup.2/g. The stoichiometry of the
comparative mixed oxide was Mo.sub.12V.sub.4O.sub.x (the respective
mixed oxide stoichiometry was analyzed for this document by optical
emission spectroscopy with inductively coupled plasma (ICP-OES)
using an ICP Optima 3000 measuring instrument from Perkin Elmer,
D-63110 Rodgau; for this purpose, 20 mg of the oxidic composition
to be analyzed in each case were dissolved with 20 ml of a 2 molar
aqueous sodium hydroxide solution (NaOH of the super pure purity
grade from Merck, Darmstadt); the clear solution resulting in each
case was subsequently diluted for the ICP-OES analysis with water
in a weight ratio of 1 (solution) to 100 (water)). d) Analysis of
the catalytic performance of the finely divided comparative mixed
oxide from 1.c) in long-term operation of a partial oxidation of
acrolein to acrylic acid heterogeneously catalyzed by the
comparative mixed oxide
It is common knowledge that catalyst performance in the long-term
operation of a heterogeneously catalyzed partial oxidation can be
assessed, rather than by such a long-term operation, also by the
corresponding performance in a less time-consuming
temperature-programmed partial oxidation experiment (TPPE).
In such an experiment, a catalyst sample present in a reactor is
exposed to a constant flow of a reaction gas mixture (constant flow
rate, constant composition of the reaction gas mixture), and the
temperature of the catalyst sample (of the finely divided active
composition sample) is simultaneously varied in a controlled manner
with time. The products and reactants leaving the reactor as a
function of the temperature of the catalyst sample are observed.
The proportions by volume thereof in the product gas mixture can be
used to obtain, as a function of the respective temperature of the
catalyst sample, characteristic parameters such as reactant
conversion, selectivity of target product formation and yield of
target product (based in each case on a single pass of the reaction
gas mixture through the catalyst bed), which enable statements
about the catalyst performance. By repeatedly running through the
temperature program up to the region of elevated temperatures,
which already cause marked total oxidation, the catalyst (the
active composition) is deliberately exposed to elevated thermal
stress over limited time periods, as a result of which the
evolution of performance thereof over multiple runs through the
temperature program enables an assessment of the long-term
characteristics thereof in normal partial oxidation operation (cf.
also WO 2005/047226 A1, "Long-term operation of a heterogeneously
catalyzed gas phase partial oxidation of acrolein to acrylic
acid").
In the TPPEs of this document, the reactor used was a hollow quartz
glass cylinder which had been bent to a U-tube and introduced into
a forced-air oven. The oven was electrically heatable and consisted
of an aluminum housing in which there was a circular cylindrical
ceramic sleeve open at the top and bottom, around which was wound
heating wire, and in the interior of which the U-tube was
positioned. It was possible to implement either variable heating
rates or temperatures constant over time. To prevent the formation
of a temperature gradient in the oven, an electrically operated
propeller was mounted at the base thereof (below the ceramic
sleeve), which brought about constant air circulation in the oven.
For the purposes of cooling the reactor, cold gas could be fed
directly into the oven interior. In addition, a cooling coil was
introduced into the aluminum casing of the oven, through which
cooling water could be conducted (a more detailed description of
the forced-air oven/reactor construction can be found in S. Endres,
Thesis, TU Darmstadt, 2009 and in J. Kunert, Thesis, TU Darmstadt
2003). The internal diameter of the quartz glass reactor tube was
0.4 cm. The wall thickness of the quartz glass was 1 mm. The two
legs of the U-tube each had a length of 14 cm and were directed
upward. The distance between the two legs was 3.3 cm.
For the performance of a TPPE, 50 mg in each case of the finely
divided active composition to be analyzed were fixed between two
glass wool plugs in the interior of the left-hand tube leg of the
U-tube reactor (in the lower third of the tube leg length). For
regulation of the temperature of the catalyst bed present in the
reactor, a thermocouple was positioned in the middle thereof (K
type, from TMH GmbH, in D-63477 Maintal).
The gas (mixture) to be supplied in each case, in the course of a
temperature-programmed partial oxidation experiment (TPPE), was
supplied to the orifice of the neck of the right-hand leg of the
U-tube reactor. The feed temperature was, unless explicitly stated
otherwise, 170.degree. C. throughout. The volume flow rate of the
gas (mixture) to be supplied in each case in all experiments was
constant at 20 ml/min over the total duration of the experiment.
The temperature of the catalyst sample present in the reactor was
varied within the range between 100.degree. C. and 480.degree.
C.
In order to put the finely divided mixed oxide to be subjected to
the temperature-programmed partial oxidation experiment into a
comparable starting state in each case (cf. WO 2005/047226 A1), it
was first of all subjected in each case to a regenerative oxidative
pretreatment while present in the reactor (referred to hereinafter
as preoxidation).
For this purpose, a regeneration gas mixture (20 ml/min) was
supplied (the feed temperature was likewise 170.degree. C.), which
consisted of 90% by volume of He and 10% by volume of molecular
oxygen. The temperature of the finely divided mixed oxide sample
was increased at a rate of 20.degree. C./min from 25.degree. C. to
400.degree. C. This temperature was subsequently maintained for 60
min, as was the regeneration gas mixture stream. Then, under a gas
stream (20 ml/min) consisting only of He (feed
temperature=100.degree. C.), the mixed oxide sample was cooled in
an essentially linear manner to a temperature of 100.degree. C.
within 30 min.
While retaining the temperature of 100.degree. C., this was
followed by purging with the actual reaction gas mixture stream (20
ml/min), the feed temperature of which was likewise 100.degree. C.,
during a ten minute run-in phase. In the case of the comparative
mixed oxide Mo.sub.12V.sub.4O.sub.x, in the case of the present
comparative example 1.d), this had the following composition: 5% by
vol. of acrolein, 10% by vol. of molecular oxygen, and 85% by vol.
of helium.
The run-in phase was then followed by the actual TPPE.
For this purpose, while retaining the reaction gas mixture stream
(20 ml/min, now feed temperature=170.degree. C.), the temperature
of the mixed oxide sample was heated at a heating rate of
10.degree. C./min from 100.degree. C. to 480.degree. C. Then
cooling was effected in an essentially linear manner to 400.degree.
C. under a pure He gas stream (inert gas stream) within 15 min
(feed temperature=170.degree. C.). This temperature was maintained
for a period of 30 min and, during this period, regeneration was
effected with the regeneration gas stream consisting of 90% by
volume of He and 10% by volume of molecular oxygen (feed
temperature=170.degree. C.). Then the mixed oxide sample was cooled
in an essentially linear manner to a temperature of 100.degree. C.
under a gas stream consisting solely of He (feed
temperature=100.degree. C.) within 30 min. This step completed the
first TP partial oxidation cycle conducted after the preoxidation
(including run-in phase).
There followed two further, identically executed TP partial
oxidation cycles (including a respective run-in phase).
The product gas mixture was analyzed online with the aid of a mass
spectrometer, to which the product gas mixture was supplied.
The mass spectrometer was a GAM 400 quadrupole mass spectrometer
from InProcess Instruments in D-28201 Bremen. It had an intake
system (quartz glass capillary) heatable to 200.degree. C. and a
cross beam ion source for electron impact ionization with
ionization energy 70 eV and an SEM detector.
The temperature signal measured by means of the thermocouple
present in the catalyst bed, and the proportions by volume of the
product gas mixture, were recorded synchronously. In the assignment
of "product gas mixture" and "temperature of the catalyst bed" it
was taken into account that the conduction distance between
catalyst bed and mass spectrometer, and within the mass
spectrometer, for the product gas mixture caused a time delay
(further details of experimental setup can be found in S. Endres,
Thesis, TU Darmstadt, 2009).
In the first two TP partial oxidation cycles, in the case of the
comparative mixed oxide Mo.sub.12V.sub.4O.sub.x, the maximum yield
Y.sup.AA of acrylic acid was attained at a catalyst bed temperature
of 330.degree. C. The value thereof was 77 mol %. As early as in
the third TP partial oxidation cycle, the maximum yield Y.sup.AA of
acrylic acid fell to 74 mol % and was at a catalyst bed temperature
of only 320.degree. C. These two decreases show that catalyst
performance in long-term operation is not very stable in
comparative terms. FIG. 2 of this document shows the plot of the
yield Y.sup.AA of acrylic acid which results in each case as a
function of the respective catalyst bed temperature both for the
first (reference numeral 1 in FIG. 2) and the third (reference
numeral 3 in FIG. 2) TP partial oxidation cycle. The abscissa of
FIG. 2 shows the temperature of the catalyst bed in .degree. C.,
and the ordinate shows the yield Y.sup.AA in mol %/100. 2.
Hydrothermal preparation of an inventive multimetal oxide of the
stoichiometry Mo.sub.12V.sub.3W.sub.2.25O.sub.x and analysis of the
performance thereof in long-term operation of a partial oxidation
of acrolein to acrylic acid heterogeneously catalyzed thereby a)
Preparation of the aqueous mixture for hydrothermal treatment
First 10 g (=56.6 mmol of Mo) of ammonium heptamolybdate
tetrahydrate and then 2.9 g (=10.6 mmol of W) of ammonium
metatungstate hydrate
[(NH.sub.4).sub.6H.sub.2W.sub.12O.sub.41.18H.sub.2O] were dissolved
at 25.degree. C. in 120 ml of water. After the resulting yellow
solution had been stirred at 25.degree. C. for a further 30
minutes, it formed a first aqueous solution.
By dissolving 3.69 g (=14.2 mmol of V) of a vanadyl sulfate hydrate
in 120 ml of water at 25.degree. C., a second aqueous solution was
prepared. While constantly stirring the first aqueous solution,
with maintenance of the 25.degree. C., the second aqueous solution
was continuously added dropwise to the first aqueous solution
within 15 minutes. The color of the resulting aqueous solution was
violet. Over 30 further minutes, it was stirred at 25.degree. C.
Subsequently, the pH of the mixed solution was adjusted to the
value of 2.2 by adding dilute aqueous sulfuric acid (the
concentration of which was about 1 molar).
All aforementioned working steps were conducted under air. Finally,
the molecular oxygen present dissolved in the resulting acidic
mixed solution was displaced by bubbling a nitrogen stream at
25.degree. C. through it for 10 minutes (.gtoreq.99.9 mol % of
N.sub.2; approx. 1500 ml/h).
The aqueous final solution thus obtained was subsequently
hydrothermally treated as described below. b) Hydrothermal
treatment of the aqueous final solution obtained in 2.a)
The aqueous solution obtained in 2.a) was treated hydrothermally as
described for the aqueous final solution obtained in 1.a). The
suspended solids were removed by filtration from the resulting
aqueous suspension, in a manner corresponding to that described in
1.b), washed with aqueous oxalic acid, then washed with water, and
finally dried in a forced-air drying cabinet to give the precursor
composition for thermal treatment. c) Thermal treatment
(calcination) of the precursor composition obtained in 2.b)
The thermal treatment of the precursor composition obtained in 2.b)
was effected like the thermal treatment (calcination) of the
precursor composition obtained in 1.b) in 1.c).
The particle sizes of the resulting multimetal oxide were in the
range of 3 to 25 .mu.m (longest dimension). The specific surface
area SA was 36 m.sup.2/g (without conducting the washing with the
aqueous oxalic acid/water in 2.b), SA was 35 m.sup.2/g). The
stoichiometry of the multimetal oxide prepared in accordance with
the invention was Mo.sub.12V.sub.3W.sub.2.25O.sub.x.
The X-ray diffractogram thereof is shown by FIGS. 3 and 4 of this
document with a different scale for the absolute intensity. The
abscissa shows the diffraction angle on the 2.THETA. scale
[degrees]. The absolute intensity is plotted on the ordinate. On
the basis of the presence of individual defined reflections, the
structure is not X-ray-amorphous. A crystalline assignment is
likewise not possible. The multimetal oxide powder can thus be
described as semicrystalline.
SEM images (1000-fold magnification) of the multimetal oxide
conducted on a DSM 962 scanning electron microscope from Carl Zeiss
in D-73447 Oberkochen (the instrument had, for surface imaging,
both an SE (secondary electrons) and a BSE ((back-scattered
electrons) detector, and an EDX detector for elemental analysis)
showed a sponge-like structure (irregularly roughened surface
peppered with crystals). The surface consisted of rod-shaped
crystals which had a length of approx. 1 .mu.m. d) analysis of the
catalytic performance of the finely divided inventive multimetal
oxide from 2.c) in long-term operation of a partial oxidation of
acrolein to acrylic acid heterogeneously catalyzed by the inventive
multimetal oxide
For the purpose of assessing the catalyst performance in long-term
operation of a correspondingly catalyzed partial oxidation of
acrolein to acrylic acid, the TPPE comprising 3 TP partial
oxidation cycles from 1.d) was repeated using the multimetal oxide
from 2.c) as the catalytic active composition.
In the first partial oxidation cycle, the maximum yield Y.sup.AA of
acrylic acid was attained at a catalyst bed temperature of
322.degree. C. The value thereof was 79 mol %. In the two
subsequent cycles, the maximum yield Y.sup.AA rose to 81 mol % and
was at a catalyst bed temperature of 325.degree. C. This stable
TPPE behavior indicates marked stability of catalyst performance in
long-term operation. Activity and selectivity of acrylic acid
formation actually experience a small increase over the three TP
partial oxidation cycles (without conducting the washing with the
aqueous oxalic acid/water, the maximum yield Y.sup.AA in the third
cycle was 73 mol %; the corresponding catalyst bed temperature was
350.degree. C.; the catalyst performance was stable over all three
cycles). 3. Noninventive preparation of a comparative multimetal
oxide of the stoichiometry Mo.sub.12V.sub.3W.sub.2.25O.sub.x
according to a prior art process and analysis of the performance
thereof in the long-term operation of a partial oxidation of
acrolein to acrylic acid heterogeneously catalyzed thereby. a)
Preparation of an aqueous starting solution
In a glass round-bottom flask which had a capacity of 2 l, 41.998 g
(=237.8 mmol of Mo) of ammonium molybdate tetrahydrate, 6.956 g
(=59.5 mol of V) of ammonium metavanadate (NH.sub.4VO.sub.3) and
11.047 g (=44.6 mmol of W) of ammonium metatungstate hydrate were
stirred in the sequence mentioned into a 1.5 l initial charge of
water at a temperature of 25.degree. C. By adding 60% by weight
aqueous nitric acid, the pH of the aqueous mixture was adjusted to
a value of 5. This was followed by stirring under reflux for
another 90 minutes and then cooling to 25.degree. C. The result was
a clear yellow/orange aqueous solution. b) Spray-drying of the
aqueous solution obtained in 3.a)
The spray drying system used is described in J. Kunert, Thesis, TU
Darmstadt 2003.
The aqueous solution to be spray-dried was initially charged at a
temperature of 25.degree. C. in an unstirred reservoir vessel. An
HPLC pump (P700 type, from LATEK Labortechnik GmbH, D-69214
Eppelheim) was used to convey the aqueous solution at a volume flow
rate of 12 ml/min into the two-phase nozzle of the spray tower. In
the nozzle, the solution was atomized by a compressed air stream
(607.8 kPa) and entrained by a hot (275.degree. C.) dry air stream
which was produced by a hot air blower (from Leister Process
Technologies, CH-6056 Kaegiswil, Vulcan "E" type, 65 dB (A), static
pressure 0.4 kPa, power: 9.9 to 13.3 kW), and dried to give a
yellow pulverulent solid which was deposited in a cyclone. The
nozzle diameter of the two-phase nozzle was 0.7 mm. The exit
temperature from the drying tower was 90.degree. C. c) Thermal
treatment (calcination) of the spray powder obtained in 3.b)
The thermal treatment of the spray powder obtained in 3.b) was
effected as described in 1.c) for the precursor composition
produced in 1.b).
However, the temperature program was configured as follows. First
of all, heating was effected at a heating rate of 2.degree. C./min
to 325.degree. C. This temperature was then maintained over 4 h.
Thereafter, the temperature was increased at a heating rate of
2.degree. C./min to 400.degree. C. and this temperature was
maintained over 10 min. Finally, the calcination material was
cooled to 25.degree. C. in an essentially linear manner within 10
h.
The particle sizes of the resulting comparative multimetal oxide
were .ltoreq.13 .mu.m (longest dimension). The specific surface
area SA was 4 m.sup.2/g. The stoichiometry of the comparative
multimetal oxide was Mo.sub.12V.sub.3W.sub.2.25O.sub.x.
The X-ray diffractogram thereof is shown by FIG. 5 of this
document. The abscissa shows the diffraction angle on the 2.THETA.
scale [degrees]. The absolute intensity is plotted on the ordinate.
On the basis of the absence of defined reflections, the multimetal
oxide powder can be regarded as X-ray-amorphous.
SEM images of the multimetal oxide showed spherical particles with
a smooth surface. Such formation of hollow spheres is a known
phenomenon for spray-drying operations. d) Analysis of the
catalytic performance of the finely divided noninventive multimetal
oxide from 3.c) in the long-term operation of a partial oxidation
of acrolein to acrylic acid heterogeneously catalyzed by this
comparative multimetal oxide
For the purpose of assessing catalyst performance in the long-term
operation of a correspondingly catalyzed partial oxidation of
acrolein to acrylic acid, the TPPE comprising three TP partial
oxidation cycles from 1.d) was repeated using the comparative
multimetal oxide from 3.c) as the catalytic active composition.
Over the three TP partial oxidation cycles, no decrease in the
maximum yield Y.sup.AA of acrylic acid was observed. In the third
TP partial oxidation cycle, the maximum yield Y.sup.AA was at a
catalyst bed temperature of 442.degree. C. and was 49 mol %. 4.
Noninventive preparation of a comparative multimetal oxide of the
stoichiometry Mo.sub.12V.sub.3W.sub.2.25O.sub.x and analysis of the
performance thereof in the long-term operation of a partial
oxidation of acrolein to acrylic acid heterogeneously catalyzed
thereby a) The preparation of the aqueous final solution from 2.a)
was repeated. b) The aqueous solution obtained in 4.a) was
spray-dried. The spray drying was effected like the spray drying of
the aqueous solution obtained in 3.a) in 3.b). c) The spray powder
obtained in 4.b) was calcined. The thermal treatment (the
calcination) was effected like the thermal treatment of the
precursor composition obtained in 2.b) in 2.c). The resulting
finely divided comparative multimetal oxide had the stoichiometry
Mo.sub.12V.sub.3W.sub.2.25O.sub.x. The specific surface area SA
thereof was 5.8 m.sup.2/g. d) The analysis of the catalytic
performance of the finely divided comparative multimetal oxide from
4.c) was effected as in 2.d) for the finely divided inventive
multimetal oxide from 2.c). Over the three TP partial oxidation
cycles, no decrease in the maximum yield Y.sup.AA of acrylic acid
was observed. In the third TP partial oxidation cycle, the maximum
yield Y.sup.AA was at a catalyst bed temperature of 400.degree. C.
and was 40 mol %. 5. Inventive preparation of a multimetal oxide of
the stoichiometry Mo.sub.12V.sub.3W.sub.2.25O.sub.x by inventive
hydrothermal aftertreatment of the comparative multimetal oxide
from 3.c) and analysis of the performance thereof in the Long-Term
operation of a partial oxidation of acrolein to acrylic acid
heterogeneously catalyzed thereby
10 g of the pulverulent comparative multimetal oxide from 3.c) were
suspended in 150 ml of water, and the resulting aqueous suspension
was introduced into the reaction space of the autoclave from 1.b)
and treated hydrothermally as described in 1.b).
After cooling to 25.degree. C., an aqueous suspension was taken
from the reaction space and the solids suspended therein were
removed by means of centrifuging (a Beckmann J2/21 centrifuge was
used; JA 14 rotor, 5000 rpm, 10750 g, 10 min).
The solid sediment removed was dried in a forced-air drying cabinet
at 110.degree. C. for 120 min and subsequent triturated in a
mortar.
Stoichiometry of the resulting mixed oxide powder 5 was
Mo.sub.12V.sub.3W.sub.2.25O.sub.x within measurement accuracy. The
specific surface area SA thereof was 138 m.sup.2/g.
The corresponding X-ray diffractogram is shown in FIG. 6 of this
document. The abscissa shows the diffraction angle on the 2.THETA.
scale [degrees]. The absolute intensity is plotted on the ordinate.
There are several defined reflections with low intensity. Overall,
the specimen is merely semicrystalline.
SEM images of the multimetal oxide still showed spherical particles
with reduced agglomeration compared to the comparative multimetal
oxide from 3.c).
For the purpose of assessing the catalyst performance in long-term
operation, the TPPE from 1.d) comprising 3 TP partial oxidation
cycles was repeated using mixed oxide powder 5 as the active
composition. Over the three TP partial oxidation cycles, no
decrease in the maximum yield Y.sup.AA of acrylic acid was
observed. In the third TP partial oxidation cycle, the maximum
yield Y.sup.AA was at a catalyst bed temperature of 351.5.degree.
C. and was 63.5 mol %.
FIG. 7 of this document shows the plot of the yield Y.sup.AA of
acrylic acid which results in each case as a function of the
respective catalyst bed temperature in the third TP partial
oxidation cycle, for the long-term operation both from 2.d)
(reference numeral 1 in FIG. 7) and from 3.d) (reference numeral 2
in FIG. 7), and from 5. (reference numeral 3 in FIG. 7). The
abscissa of FIG. 7 shows the temperature of the catalyst bed in
.degree. C., and the ordinate shows the yield Y.sup.AA in mol
%/100. 6. Analysis of the catalytic performance of the finely
divided inventive multimetal oxide from 2.c) in the long-term
operation of a partial oxidation of acrolein to acrylic acid
heterogeneously catalyzed by this multimetal oxide
The procedure was as in 2.d). The reaction gas mixture stream,
however, had the following composition: 5% by vol. of acrolein, 10%
by vol. of molecular oxygen, 7% by vol. of H.sub.2O, and 78% by
vol. of helium.
The maximum yield Y.sup.AA was essentially unchanged over the three
TP partial oxidation cycles. It was 89 mol % in the third partial
oxidation cycle and was attained at a catalyst bed temperature of
300.degree. C. 7. Analysis of the catalytic performance of the
finely divided inventive multimetal oxide from 5. in the long-term
operation of a partial oxidation of acrolein to acrylic acid
heterogeneously catalyzed by this multimetal oxide
The procedure was as in 5. The reaction gas mixture stream,
however, had the following composition: 5% by vol. of acrolein, 10%
by vol. of molecular oxygen, 7% by vol. of H.sub.2O, and 78% by
vol. of helium.
The maximum yield Y.sup.AA was essentially unchanged over the three
TP partial oxidation cycles. It was 74 mol % in the third partial
oxidation cycle and was attained at a catalyst bed temperature of
324.degree. C. 8. Analysis of the catalytic performance of the
finely divided inventive multimetal oxide from 2.c) and of the
finely divided noninventive multimetal oxide from 3.c) in the
long-term operation of partial oxidations of methacrolein to
methacrylic acid heterogeneously catalyzed by these multimetal
oxides a) The procedure was as in 2.d) or as in 3.d). The reaction
gas mixture stream, however, had the following composition: 5% by
vol. of methacrolein, 10% by vol. of molecular oxygen, and 85% by
vol. of helium.
The ratio of the maximum yields Y.sup.MA of methacrylic acid
established in the third TP partial oxidation cycle in each case
was Y.sup.MA(2.d):Y.sup.MA(3.d)=2.2.
In the case of use of the inventive multimetal oxide from 2.c), the
maximum in the methacryclic acid yield in the third TP partial
oxidation cycle was established at a catalyst bed temperature of
360.degree. C.
In the case of use of the noninventive comparative multimetal oxide
from 3.c), the maximum in the methacrylic acid yield in the third
TP partial oxidation cycle was established at a catalyst bed
temperature of 417.degree. C. b) The TPPE from 8.a) with the
inventive multimetal oxide from 2.c) was repeated, except that the
reaction gas mixture stream had the following composition: 5% by
vol. of methacrolein, 10% by vol. of molecular oxygen, 7% by vol.
of H.sub.2O, and 78% by vol. of helium.
Compared to the maximum yield Y.sup.MA of methacrylic acid achieved
in the third cycle of the TPPE from 8.a), the maximum yield of
methacrylic acid in the third cycle of the TPPE in 8.b) was greater
by a factor of 1.41. It was established at a catalyst bed
temperature of 350.degree. C. 9. Preparation of an eggshell
catalyst EC1 with an inventive catalytically active multimetal
oxide composition of the stoichiometry
mo.sub.12v.sub.3.3w.sub.3.24o.sub.x (in the details given below,
any hydrate water present is not addressed explicitly)
In a glass 4-neck flask which had a capacity of 4 I and which was
equipped with a stirrer apparatus, 87.2 g of ammonium
heptamolybdate (=495.3 mmol of Mo, from H. C. Starck GmbH) were
dissolved in 1.046 l of water, the temperature of which was
25.degree. C., while maintaining the 25.degree. C. Thereafter, 24.7
g of ammonium paratungstate (=95.4 mmol of W, from BASF SE) were
added and the resulting aqueous mixture was stirred at 80.degree.
C. for 30 minutes. The resulting solution at 80.degree. C.
constituted solution I.
33.9 g of vanadyl sulfate (=127.2 mmol of V, from Fischer
Scientific) were added to 1.046 l of water at a temperature of
80.degree. C., and dissolved to give solution II while stirring and
maintaining the 80.degree. C.
While maintaining the 80.degree. C., solution II was stirred into
solution I. Then the mixture was cooled to 25.degree. C. The pH of
the resulting solution was adjusted to 2.0 by adding 1 molar
sulfuric acid while stirring. Thereafter, the molecular oxygen
dissolved in the solution was displaced by passing molecular
nitrogen through (the O.sub.2 content of the N.sub.2 was <10 ppm
by vol.) for 10 minutes.
Subsequently, the solution was introduced under air into the
non-Teflon-lined stirred reaction space of an autoclave
(constructed in-house by BASF SE). The reaction space had a
capacity of 3.5 l and had a shell manufactured from Hastelloy C. A
thermocouple projected into the reaction space for temperature
monitoring. The air present in the gas phase of the filled
autoclave was subsequently displaced with molecular nitrogen. For
this purpose, three times in succession, the autoclave was filled
with 5 bar nitrogen (the O.sub.2 content of which was <20 ppm by
vol.) and immediately decompressed again to ambient pressure each
time. Thereafter, the autoclave was heated to 175.degree. C. at a
heating rate of 5.degree. C./min while stirring (rotation rate: 500
rpm). This temperature was maintained while stirring for 24 hours.
Then, while continuing to stir, cooling was effected to 25.degree.
C. in an essentially linear manner within 2.5 hours, and then
purging was effected again, three times in succession with
molecular nitrogen (<20 ppm by vol. of O.sub.2). For this
purpose, the pressure in the autoclave was brought to 5 bar in each
case with the nitrogen and, on attainment of the 5 bar, released
again immediately to ambient pressure (atmospheric pressure). Then
the autoclave was opened and the aqueous suspension present was
sucked out of the autoclave through a ceramic suction filter (from
Witeg Labortechnik GmbH, D-97877 Wertheim, pore size 4), and the
filtercake obtained was dried in a forced-air drying cabinet at
80.degree. C. for 16 h. The dried filtercake was slurried in 1 l of
a 0.4 molar (based on standard conditions) solution of oxalic acid
in water at 70.degree. C. by stirring, and then stirred at
70.degree. C. for 1 h (rotation rate: 300 rpm). Then the mixture
was filtered with suction again through a ceramic suction filter
(from Witeg Labortechnik GmbH, D-97877 Wertheim, pore size 4). The
resulting filtercake was washed three times with 100 ml each time
of water at 25.degree. C., and finally dried again at 80.degree. C.
in a forced-air drying cabinet for 16 h (to cover the demand for
precursor composition, the preparation method described so far was
reproduced 12 times).
The entire amount of precursor composition taken from the
forced-air drying cabinet was subsequently ground in a ZM 200 mill
from Retsch to give a fine powder, of which 50% of the powder
particles passed through a sieve of mesh size 1 to 10 .mu.m and in
which the numerical proportion of particles having a longest
dimension above 50 .mu.m was less than 1% (a particle diameter
distribution particularly suitable in accordance with the invention
at this point is shown in FIG. 3 of DE 102007010422 A1).
The thermal treatment (calcination) of the finely divided precursor
composition was effected in 180 g portions in a rotary sphere oven
as shown in FIG. 1 of DE 10033121 A1. The rotary sphere oven
consisted of a 1 l quartz glass round-bottom flask on a rotary
evaporator. The round-bottom flask was in an oven. Over the entire
calcination (including cooling), a gas stream of 50 l (STP)/h (the
l (STP) relate here to 25.degree. C. and 101.3 kPa) of molecular
nitrogen (<10 ppm by vol. of O.sub.2) was passed through the
rotary tube. This was supplied to the rotary tube oven with a
temperature of 25.degree. C. During the calcination, the
round-bottom flask rotated at a rotation rate of 7 rpm.
Over the course of the thermal treatment, the precursor composition
present in the round-bottom flask was first of all heated from
25.degree. C. in a linear manner to a material temperature
(thermocouple-monitored) of 350.degree. C. within 70 minutes.
Subsequently, this material temperature was maintained for 1 hour.
Thereafter, the material temperature was heated in an essentially
linear manner to 450.degree. C. within 20 min, and this temperature
was maintained over 1 minute. Subsequently, the material
temperature was increased to 500.degree. C. in a linear manner
within 20 minutes, and this temperature was maintained for 2
minutes. Thereafter, the rotary sphere oven contents were cooled in
an essentially linear manner to 25.degree. C. within 2.5 h.
The finely divided catalytically active multimetal oxide
composition taken from the rotary sphere oven (the specific BET
surface area of which was 30 m.sup.2/g) was subsequently used as in
example S1 of EP 714700 A2 to coat 800 g of annular support bodies
(external diameter 7 mm, length 3 mm, internal diameter 4 mm, C220
steatite from CeramTec with a surface roughness R.sub.z of 45 .mu.m
(grit layer; name: "7.times.3.times.4 Steatite ring porous
coated")) (except that in contrast to the aforementioned example
S1, the active composition content selected was approx. 20% by
weight (based on the total weight of support body and active
composition)). The total pore volume of a support body based on the
volume of the mass of a support body was .ltoreq.1% by volume.
Binder, as in example S1 of EP 714700 A2, was an aqueous solution
of 75% by weight of water and 25% by weight of glycerol. The
coating was effected in a rotating coating drum (internal
diameter=25.5 cm; 36 rpm) which had been filled with the support
bodies. About 70 ml of liquid binder was sprayed onto the support
bodies using a nozzle (nozzle diameter=1 mm) within 40 minutes (the
exact amount of binder in each case was such that no twin bodies
were formed, but the entire amount of powder was taken up onto the
surface of the support bodies without occurrence of powder
agglomeration). At the same time, over the same period, 205 g of
the catalytically active multimetal oxide composition powder were
metered in continuously by means of a conveying screw outside the
spray cone of the atomizer nozzle. During the coating, the powder
supplied was taken up completely onto the surface of the support
bodies. No agglomeration of the finely divided oxidic active
composition was observed.
Subsequently, the coated rings were held at a temperature of
300.degree. C. in a forced-air drying cabinet for 2 h
(demoisturized). The eggshell catalysts EC1 taken from the
forced-air drying cabinet had, based on the total mass thereof, an
oxidic active composition content of 19% by weight.
The stoichiometry of the active composition shell of the eggshell
catalyst EC1 was Mo.sub.12V.sub.3.3W.sub.3.24O.sub.x. 10.
Preparation of an Eggshell Catalyst EC2 with an Inventive
Catalytically Active Multimetal Oxide Composition of the
Stoichiometry Mo.sub.12V.sub.3.2W.sub.1.9Cu.sub.0.4O.sub.x (In the
Details Given Below, Any Hydrate Water Present is Not Addressed
Explicitly))
The preparation of the annular eggshell catalyst EC2 was effected
like the preparation of the eggshell catalyst EC1. However, the
aqueous solution I comprised, rather than the 24.7 g of ammonium
paratungstate, only 13.1 g of the same substance dissolved in the
same amount of water as W source, and solution II comprised 28.3 g
of vanadyl sulfate (from Fischer Scientific) and 12.6 g of
copper(II) sulfate (=50.5 mmol of Cu, Sigma Aldrich) dissolved in
1.046 l of water.
The stoichiometry of the resulting finely divided active
composition was Mo.sub.12V.sub.3.2W.sub.1.9Cu.sub.0.4O.sub.x. The
BET surface area SA thereof after calcination was 30 m.sup.2/g and,
based on the total mass of the eggshell catalyst EC2, the oxidic
active composition content was 18.8% by weight. 11. Preparation of
a comparative eggshell catalyst CEC1 with a noninventive
catalytically active multimetal oxide composition of the
stoichiometry Mo.sub.12V.sub.3W.sub.2.25O.sub.x
450.0 g of ammonium heptamolybdate tetrahydrate (Mo content=54.5%
by weight) were dissolved in 5400 g of water at 90.degree. C.
within 5 minutes. Subsequently, while maintaining the 90.degree.
C., 82.0 g of ammonium metavanadate (V content=43.5% by weight)
were added and the resulting solution was stirred at 90.degree. C.
for a further 40 minutes. Then 175.4 g of ammonium paratungstate
heptahydrate (W content=71% by weight) were added and the resulting
solution was stirred at 90.degree. C. for a further 30 minutes.
The aqueous solution was subsequently spray-dried at an inlet
temperature of 330.degree. C. and an outlet temperature of
106.degree. C. in an air stream within 1 h (spray tower from NIRO,
spray head No. F0A1). During the spray drying, stirring of the as
yet unsprayed proportion of the suspension was continued in each
case while maintaining the 90.degree. C.
The resulting spray powder, fully corresponding to the procedure
with the spray powder in comparative example 1B of DE 102010023312
A1, was processed further to give annular comparative eggshell
catalyst CEC1 (the annular support used and the coating method
corresponded to those in "9." of this (the present) document). The
highest material temperature in the calcination was 400.degree.
C.
The stoichiometry of the active composition was
Mo.sub.12V.sub.3W.sub.2.25O.sub.x. The BET surface area SA thereof
after calcination was 13.3 m.sup.2/g and, based on the total mass
of the eggshell catalyst CEC1, the oxidic active composition
content was 20% by weight. 12. Preparation of a comparative
eggshell catalyst CEC2 with a noninventive catalytically active
multimetal oxide composition of the stoichiometry
Mo.sub.12V.sub.3W.sub.1.2Cu.sub.0.6O.sub.x
The preparation was effected as described in comparative example 1B
of DE 102010023312 A1. The aqueous solution of the elemental
constituents was spray-dried and the resulting spray powder was
processed further to give annular comparative eggshell catalysts
CEC2 (the annular support used and the coating method corresponded
to those in "9." of this (the present) document). The highest
material temperature in the calcination was 400.degree. C.
The stoichiometry of the active composition was
Mo.sub.12V.sub.3W.sub.1.2Cu.sub.0.6O.sub.x. The BET surface area SA
thereof after calcination was 15 m.sup.2/g and, based on the total
mass of the eggshell catalyst CEC1, the oxidic active composition
content was 20% by weight. 13. Testing of eggshell catalysts EC1,
EC2, CEC1 and CEC2 as catalysts for the heterogeneously catalyzed
partial gas phase oxidation of acrolein to acrylic acid
The eggshell catalysts were each tested in a reaction tube (V2A
steel; external diameter 30 mm; wall thickness 2 mm; internal
diameter 26 mm; length 465 cm) around which a salt bath flowed
(mixture of 53% by weight of potassium nitrate, 40% by weight of
sodium nitrite and 7% by weight of sodium nitrate), and which was
charged from the top downward as follows: Section 1: length 79 cm
Empty tube; Section 2: length 62 cm Preliminary bed of steatite
rings of geometry 7 mm.times.3 mm.times.4 mm (external
diameter.times.length.times.internal diameter; C220 Steatite from
CeramTec); Section 3: length 100 cm Fixed catalyst bed composed of
a homogeneous mixture consisting of 15% by weight of steatite rings
of geometry 7 mm.times.3 mm.times.4 mm (external
diameter.times.length.times.internal diameter; C220 steatite from
CeramTec) and 80% by weight of the respective eggshell catalyst;
Section 4: length 200 cm Fixed catalyst bed exclusively consisting
of the eggshell catalyst also used in section 3 in each case;
Section 5: length 10 cm Subsequent bed of the same steatite rings
as in section 2; Section 6: length 14 cm Catalyst support made from
V2A steel for accommodation of the fixed catalyst bed.
The reaction gas mixture had the following starting composition:
acrolein 4.3% by vol., propene 0.2% by vol., propane 0.2% by vol.,
acrylic acid 0.3% by vol., O.sub.2 5.4% by vol., H.sub.2O 7% by
vol., CO and CO.sub.2 0.4% by vol., and N.sub.2 82.2% by vol.
It flowed through the reaction tube from the top downward in each
case.
The acrolein space velocity (as defined in DE 19927624 A1) on the
fixed catalyst bed was set in each case to 75 l (STP)/lh.
50 kg of stirred and externally electrically heated salt melt
flowed around the length of the reaction tube (apart from the last
10 cm of the empty tube in section 1 and the last 3 cm of the tube
in section 6) (the flow rate at the tube was 3 m/s).
The salt bath temperature (T.sup.B, .degree. C.) with which the
salt bath was supplied was set in each case such that the
conversion of acrolein (C.sup.A, mol %), based on a single pass of
the reaction gas mixture through the catalyst bed, was approx. 99.2
mol %. The inlet temperature of the reaction gas mixture (at the
inlet into the reaction tube) was adjusted to the respective salt
bath temperature.
Along the reaction tube, the salt bath temperature did not change
as a result of heating (more heat was radiated from the salt bath
than released from the reaction tube to the salt bath).
Table 1 below shows the results as a function of the eggshell
catalyst used after 100 hours of operation in each case
(S.sup.AA=selectivity of acrylic acid formation):
TABLE-US-00001 TABLE 1 Eggshell catalyst T.sup.B (.degree. C.)
C.sup.A (mol %) S.sup.AA (mol %) EC1 242.4 99.1 92.6 EC2 251.0 99.2
97.0 CEC1 293.6 99.3 91.8 CEC2 270.0 99.3 97.0
* * * * *